diff --git a/.gitignore b/.gitignore
index 90d94706..4c0e6662 100644
--- a/.gitignore
+++ b/.gitignore
@@ -4,3 +4,4 @@ benchmark/
 lib/linguist/samples.json
 /grammars
 /node_modules
+test/fixtures/ace_modes.json
diff --git a/Rakefile b/Rakefile
index 470dcec9..068af0bb 100644
--- a/Rakefile
+++ b/Rakefile
@@ -3,13 +3,14 @@ require 'rake/clean'
 require 'rake/testtask'
 require 'yaml'
 require 'yajl'
+require 'open-uri'
 
 task :default => :test
 
 Rake::TestTask.new
 
-# Extend test task to check for samples
-task :test => :check_samples
+# Extend test task to check for samples and fetch latest Ace modes
+task :test => [:check_samples, :fetch_ace_modes]
 
 desc "Check that we have samples.json generated"
 task :check_samples do
@@ -18,6 +19,20 @@ task :check_samples do
   end
 end
 
+desc "Fetch the latest Ace modes from its GitHub repository"
+task :fetch_ace_modes do
+  ACE_FIXTURE_PATH = File.join('test', 'fixtures', 'ace_modes.json')
+
+  File.delete(ACE_FIXTURE_PATH) if File.exist?(ACE_FIXTURE_PATH)
+
+  begin
+    ace_github_modes = open("https://api.github.com/repos/ajaxorg/ace/contents/lib/ace/mode").read
+    File.write(ACE_FIXTURE_PATH, ace_github_modes)
+  rescue OpenURI::HTTPError, SocketError
+      # no internet? no problem.
+  end
+end
+
 task :samples do
   require 'linguist/samples'
   json = Yajl.dump(Linguist::Samples.data, :pretty => true)
diff --git a/lib/linguist/languages.yml b/lib/linguist/languages.yml
index f601aa78..04c60eb4 100644
--- a/lib/linguist/languages.yml
+++ b/lib/linguist/languages.yml
@@ -3,7 +3,9 @@
 # type              - Either data, programming, markup, prose, or nil
 # aliases           - An Array of additional aliases (implicitly
 #                     includes name.downcase)
-# ace_mode          - A String name of Ace Mode (if available)
+# ace_mode          - A String name of the Ace Mode used for highlighting whenever
+#                     a file is edited. This must match one of the filenames in http://git.io/3XO_Cg.
+#                     Use "none" if a mode does not exist.
 # wrap              - Boolean wrap to enable line wrapping (default: false)
 # extensions        - An Array of associated extensions (the first one is
 #                     considered the primary extension)
@@ -26,6 +28,7 @@ ABAP:
   type: programming
   extensions:
   - .abap
+  ace_mode: abap
 
 AGS Script:
   type: programming
@@ -36,12 +39,14 @@ AGS Script:
   - .asc
   - .ash
   tm_scope: source.c++
+  ace_mode: c_cpp
 
 ANTLR:
   type: programming
   color: "#9DC3FF"
   extensions:
   - .g4
+  ace_mode: none
 
 APL:
   type: programming
@@ -50,6 +55,7 @@ APL:
   - .apl
   - .dyalog
   tm_scope: none
+  ace_mode: none
 
 ASP:
   type: programming
@@ -66,6 +72,7 @@ ASP:
   - .asmx
   - .aspx
   - .axd
+  ace_mode: none
 
 ATS:
   type: programming
@@ -78,6 +85,7 @@ ATS:
   - .hats
   - .sats
   tm_scope: source.ocaml
+  ace_mode: ocaml
 
 ActionScript:
   type: programming
@@ -90,6 +98,7 @@ ActionScript:
   - as3
   extensions:
   - .as
+  ace_mode: actionscript
 
 Ada:
   type: programming
@@ -100,18 +109,21 @@ Ada:
   - .ads
   aliases:
   - ada95ada2005
+  ace_mode: ada
 
 Agda:
   type: programming
   color: "#467C91"
   extensions:
   - .agda
+  ace_mode: none
 
 Alloy:
   type: programming  # 'modeling' would be more appropiate
   color: "#cc5c24"
   extensions:
   - .als
+  ace_mode: none
 
 Ant Build System:
   type: data
@@ -119,6 +131,7 @@ Ant Build System:
   filenames:
   - ant.xml
   - build.xml
+  ace_mode: xml
 
 ApacheConf:
   type: markup
@@ -129,12 +142,14 @@ ApacheConf:
   - .apacheconf
   - .conf
   tm_scope: source.apache-config
+  ace_mode: apache_conf
 
 Apex:
   type: programming
   extensions:
   - .cls
   tm_scope: source.java
+  ace_mode: java
 
 AppleScript:
   type: programming
@@ -145,6 +160,7 @@ AppleScript:
   - .scpt
   interpreters:
   - osascript
+  ace_mode: applescript
 
 Arc:
   type: programming
@@ -152,6 +168,7 @@ Arc:
   extensions:
   - .arc
   tm_scope: none
+  ace_mode: none
 
 Arduino:
   type: programming
@@ -159,6 +176,7 @@ Arduino:
   extensions:
   - .ino
   tm_scope: source.c++
+  ace_mode: c_cpp
 
 AsciiDoc:
   type: prose
@@ -176,6 +194,7 @@ AspectJ:
   extensions:
   - .aj
   tm_scope: none
+  ace_mode: none
 
 Assembly:
   type: programming
@@ -188,12 +207,14 @@ Assembly:
   - .ASM
   - .a51
   tm_scope: source.asm.x86
+  ace_mode: assembly_x86
 
 Augeas:
   type: programming
   extensions:
   - .aug
   tm_scope: none
+  ace_mode: none
 
 AutoHotkey:
   type: programming
@@ -204,6 +225,7 @@ AutoHotkey:
   - .ahk
   - .ahkl
   tm_scope: none
+  ace_mode: autohotkey
 
 AutoIt:
   type: programming
@@ -215,6 +237,7 @@ AutoIt:
   extensions:
   - .au3
   tm_scope: source.autoit.3
+  ace_mode: autohotkey
 
 Awk:
   type: programming
@@ -229,6 +252,7 @@ Awk:
   - gawk
   - mawk
   - nawk
+  ace_mode: none
 
 Batchfile:
   type: programming
@@ -243,16 +267,19 @@ Batchfile:
   - .bat
   - .cmd
   tm_scope: source.dosbatch
+  ace_mode: batchfile
 
 Befunge:
   extensions:
   - .befunge
+  ace_mode: none
 
 Bison:
   type: programming
   tm_scope: source.bison
   extensions:
   - .y
+  ace_mode: none
 
 BlitzBasic:
   type: programming
@@ -265,6 +292,7 @@ BlitzBasic:
   - .bb
   - .decls
   tm_scope: source.blitzmax
+  ace_mode: none
 
 BlitzMax:
   type: programming
@@ -273,35 +301,41 @@ BlitzMax:
   - .bmx
   aliases:
   - bmax
+  ace_mode: none
 
 Bluespec:
   type: programming
   extensions:
   - .bsv
   tm_scope: source.verilog
+  ace_mode: verilog
 
 Boo:
   type: programming
   color: "#d4bec1"
   extensions:
   - .boo
+  ace_mode: none
 
 Brainfuck:
   extensions:
   - .b
   - .bf
   tm_scope: source.bf
+  ace_mode: none
 
 Brightscript:
   type: programming
   extensions:
   - .brs
   tm_scope: none
+  ace_mode: none
 
 Bro:
   type: programming
   extensions:
   - .bro
+  ace_mode: none
 
 C:
   type: programming
@@ -314,6 +348,7 @@ C:
   - .h
   - .idc
   - .w
+  ace_mode: c_cpp
 
 C#:
   type: programming
@@ -355,6 +390,7 @@ C-ObjDump:
   extensions:
   - .c-objdump
   tm_scope: objdump.x86asm
+  ace_mode: assembly_x86
 
 C2hs Haskell:
   type: programming
@@ -364,12 +400,14 @@ C2hs Haskell:
   extensions:
   - .chs
   tm_scope: source.haskell
+  ace_mode: haskell
 
 CLIPS:
   type: programming
   extensions:
   - .clp
   tm_scope: none
+  ace_mode: none
 
 CMake:
   extensions:
@@ -377,6 +415,7 @@ CMake:
   - .in
   filenames:
   - CMakeLists.txt
+  ace_mode: none
 
 COBOL:
   type: programming
@@ -388,6 +427,7 @@ COBOL:
   - .ccp
   - .cobol
   - .cpy
+  ace_mode: cobol
 
 CSS:
   ace_mode: css
@@ -400,11 +440,13 @@ Cap'n Proto:
   tm_scope: source.capnp
   extensions:
   - .capnp
+  ace_mode: none
 
 Ceylon:
   type: programming
   extensions:
   - .ceylon
+  ace_mode: none
 
 Chapel:
   type: programming
@@ -413,11 +455,13 @@ Chapel:
   - chpl
   extensions:
   - .chpl
+  ace_mode: none
 
 ChucK:
   extensions:
   - .ck
   tm_scope: source.java
+  ace_mode: java
 
 Cirru:
   type: programming
@@ -433,6 +477,7 @@ Clean:
   - .icl
   - .dcl
   tm_scope: none
+  ace_mode: none
 
 Clojure:
   type: programming
@@ -515,6 +560,7 @@ Common Lisp:
   - ccl
   - clisp
   - ecl
+  ace_mode: lisp
 
 Component Pascal:
   type: programming
@@ -526,18 +572,21 @@ Component Pascal:
   aliases:
   - delphi
   - objectpascal
+  ace_mode: pascal
 
 Cool:
   type: programming
   extensions:
   - .cl
   tm_scope: source.cool
+  ace_mode: none
 
 Coq:
   type: programming
   extensions:
   - .coq
   - .v
+  ace_mode: none
 
 Cpp-ObjDump:
   type: data
@@ -550,6 +599,7 @@ Cpp-ObjDump:
   tm_scope: objdump.x86asm
   aliases:
   - c++-objdumb
+  ace_mode: assembly_x86
 
 Creole:
   type: prose
@@ -557,6 +607,7 @@ Creole:
   extensions:
   - .creole
   tm_scope: none
+  ace_mode: none
 
 Crystal:
   type: programming
@@ -573,6 +624,7 @@ Cucumber:
   tm_scope: text.gherkin.feature
   aliases:
   - gherkin
+  ace_mode: none
 
 Cuda:
   type: programming
@@ -580,12 +632,14 @@ Cuda:
   - .cu
   - .cuh
   tm_scope: source.cuda-c++
+  ace_mode: c_cpp
 
 Cycript:
   type: programming
   extensions:
   - .cy
   tm_scope: source.js
+  ace_mode: javascript
 
 Cython:
   type: programming
@@ -596,6 +650,7 @@ Cython:
   - .pxi
   aliases:
   - pyrex
+  ace_mode: none
 
 D:
   type: programming
@@ -603,12 +658,14 @@ D:
   extensions:
   - .d
   - .di
+  ace_mode: d
 
 D-ObjDump:
   type: data
   extensions:
   - .d-objdump
   tm_scope: objdump.x86asm
+  ace_mode: assembly_x86
 
 DM:
   type: programming
@@ -618,6 +675,7 @@ DM:
   aliases:
   - byond
   tm_scope: source.c++
+  ace_mode: c_cpp
 
 Darcs Patch:
   search_term: dpatch
@@ -627,12 +685,14 @@ Darcs Patch:
   - .darcspatch
   - .dpatch
   tm_scope: none
+  ace_mode: none
 
 Dart:
   type: programming
   color: "#98BAD6"
   extensions:
   - .dart
+  ace_mode: dart
 
 Diff:
   extensions:
@@ -640,6 +700,7 @@ Diff:
   - .patch
   aliases:
   - udiff
+  ace_mode: diff
 
 Dockerfile:
   type: data
@@ -648,6 +709,7 @@ Dockerfile:
   - .dockerfile
   filenames:
   - Dockerfile
+  ace_mode: dockerfile
 
 Dogescript:
   type: programming
@@ -655,6 +717,7 @@ Dogescript:
   extensions:
   - .djs
   tm_scope: none
+  ace_mode: none
 
 Dylan:
   type: programming
@@ -664,6 +727,7 @@ Dylan:
   - .dyl
   - .intr
   - .lid
+  ace_mode: none
 
 E:
   type: programming
@@ -671,6 +735,7 @@ E:
   extensions:
   - .E
   tm_scope: none
+  ace_mode: none
 
 ECL:
   type: programming
@@ -679,6 +744,7 @@ ECL:
   - .ecl
   - .eclxml
   tm_scope: none
+  ace_mode: none
 
 Eagle:
   type: markup
@@ -687,6 +753,7 @@ Eagle:
   - .sch
   - .brd
   tm_scope: text.xml
+  ace_mode: xml
 
 Ecere Projects:
   type: data
@@ -694,12 +761,14 @@ Ecere Projects:
   extensions:
   - .epj
   tm_scope: source.json
+  ace_mode: json
 
 Eiffel:
   type: programming
   color: "#946d57"
   extensions:
   - .e
+  ace_mode: eiffel
 
 Elixir:
   type: programming
@@ -707,12 +776,14 @@ Elixir:
   extensions:
   - .ex
   - .exs
+  ace_mode: elixir
 
 Elm:
   type: programming
   extensions:
   - .elm
   tm_scope: source.haskell
+  ace_mode: elm
 
 Emacs Lisp:
   type: programming
@@ -726,6 +797,7 @@ Emacs Lisp:
   extensions:
   - .el
   - .emacs
+  ace_mode: lisp
 
 EmberScript:
   type: programming
@@ -734,6 +806,7 @@ EmberScript:
   - .em
   - .emberscript
   tm_scope: source.coffee
+  ace_mode: coffee
 
 Erlang:
   type: programming
@@ -743,6 +816,7 @@ Erlang:
   - .es
   - .escript
   - .hrl
+  ace_mode: erlang
   interpreters:
   - escript
 
@@ -757,6 +831,7 @@ F#:
   - .fsi
   - .fsx
   tm_scope: source.fsharp
+  ace_mode: none
 
 FLUX:
   type: programming
@@ -765,6 +840,7 @@ FLUX:
   - .fx
   - .flux
   tm_scope: none
+  ace_mode: none
 
 FORTRAN:
   type: programming
@@ -787,6 +863,7 @@ FORTRAN:
   - .for
   - .fpp
   tm_scope: source.fortran.modern
+  ace_mode: none
 
 Factor:
   type: programming
@@ -796,6 +873,7 @@ Factor:
   filenames:
     - .factor-boot-rc
     - .factor-rc
+  ace_mode: none
 
 Fancy:
   type: programming
@@ -805,6 +883,7 @@ Fancy:
   - .fancypack
   filenames:
   - Fakefile
+  ace_mode: none
 
 Fantom:
   type: programming
@@ -812,6 +891,7 @@ Fantom:
   extensions:
   - .fan
   tm_scope: source.fan
+  ace_mode: none
 
 Forth:
   type: programming
@@ -825,6 +905,7 @@ Forth:
   - .forth
   - .frt
   - .fs
+  ace_mode: forth
 
 Frege:
   type: programming
@@ -832,6 +913,7 @@ Frege:
   extensions:
   - .fr
   tm_scope: source.haskell
+  ace_mode: haskell
 
 G-code:
   type: data
@@ -840,12 +922,14 @@ G-code:
   - .gco
   - .gcode
   tm_scope: none
+  ace_mode: gcode
 
 GAMS:
   type: programming
   extensions:
   - .gms
   tm_scope: none
+  ace_mode: none
 
 GAP:
   type: programming
@@ -855,6 +939,7 @@ GAP:
   - .gd
   - .gi
   tm_scope: none
+  ace_mode: none
 
 GAS:
   type: programming
@@ -863,12 +948,14 @@ GAS:
   - .s
   - .S
   tm_scope: source.asm.x86
+  ace_mode: assembly_x86
 
 GDScript:
   type: programming
   extensions:
   - .gd
   tm_scope: none
+  ace_mode: none
 
 GLSL:
   group: C
@@ -888,6 +975,7 @@ GLSL:
   - .vert
   - .vrx
   - .vshader
+  ace_mode: glsl
 
 Game Maker Language:
   type: programming
@@ -895,6 +983,7 @@ Game Maker Language:
   extensions:
   - .gml
   tm_scope: source.js
+  ace_mode: javascript
 
 Genshi:
   extensions:
@@ -903,18 +992,21 @@ Genshi:
   aliases:
   - xml+genshi
   - xml+kid
+  ace_mode: xml
 
 Gentoo Ebuild:
   group: Shell
   extensions:
   - .ebuild
   tm_scope: source.shell
+  ace_mode: sh
 
 Gentoo Eclass:
   group: Shell
   extensions:
   - .eclass
   tm_scope: source.shell
+  ace_mode: sh
 
 Gettext Catalog:
   search_term: pot
@@ -925,6 +1017,7 @@ Gettext Catalog:
   - .po
   - .pot
   tm_scope: source.po
+  ace_mode: none
 
 Glyph:
   type: programming
@@ -932,6 +1025,7 @@ Glyph:
   extensions:
   - .glf
   tm_scope: source.tcl
+  ace_mode: tcl
 
 Gnuplot:
   type: programming
@@ -944,12 +1038,14 @@ Gnuplot:
   - .plt
   interpreters:
   - gnuplot
+  ace_mode: none
 
 Go:
   type: programming
   color: "#375eab"
   extensions:
   - .go
+  ace_mode: golang
 
 Golo:
   type: programming
@@ -957,6 +1053,7 @@ Golo:
   extensions:
   - .golo
   tm_scope: none
+  ace_mode: none
 
 Gosu:
   type: programming
@@ -967,18 +1064,21 @@ Gosu:
   - .gsx
   - .vark
   tm_scope: source.gosu.2
+  ace_mode: none
 
 Grace:
   type: programming
   extensions:
   - .grace
   tm_scope: none
+  ace_mode: none
 
 Gradle:
   type: data
   extensions:
   - .gradle
   tm_scope: source.groovy.gradle
+  ace_mode: none
 
 Grammatical Framework:
   type: programming
@@ -990,12 +1090,14 @@ Grammatical Framework:
   searchable: true
   color: "#ff0000"
   tm_scope: source.haskell
+  ace_mode: haskell
 
 Graph Modeling Language:
   type: data
   extensions:
   - .gml
   tm_scope: none
+  ace_mode: none
 
 Graphviz (DOT):
   type: data
@@ -1004,6 +1106,7 @@ Graphviz (DOT):
   - .dot
   - .DOT
   - .gv
+  ace_mode: none
 
 Groff:
   extensions:
@@ -1018,6 +1121,7 @@ Groff:
   tm_scope: text.groff
   aliases:
   - nroff
+  ace_mode: none
 
 Groovy:
   type: programming
@@ -1039,6 +1143,7 @@ Groovy Server Pages:
   extensions:
   - .gsp
   tm_scope: text.html.jsp
+  ace_mode: jsp
 
 HTML:
   type: markup
@@ -1064,6 +1169,7 @@ HTML+Django:
   - html+django/jinja
   - html+jinja
   - htmldjango
+  ace_mode: django
 
 HTML+ERB:
   type: markup
@@ -1074,6 +1180,7 @@ HTML+ERB:
   extensions:
   - .erb
   - .deface
+  ace_mode: html_ruby
 
 HTML+PHP:
   type: markup
@@ -1081,12 +1188,14 @@ HTML+PHP:
   group: HTML
   extensions:
   - .phtml
+  ace_mode: php
 
 HTTP:
   type: data
   extensions:
   - .http
   tm_scope: none
+  ace_mode: none
 
 Hack:
   type: programming
@@ -1102,6 +1211,7 @@ Haml:
   extensions:
   - .haml
   - .deface
+  ace_mode: haml
 
 Handlebars:
   type: markup
@@ -1111,6 +1221,7 @@ Handlebars:
   - .handlebars
   - .hbs
   tm_scope: text.html.handlebars
+  ace_mode: handlebars
 
 Harbour:
   type: programming
@@ -1118,6 +1229,7 @@ Harbour:
   extensions:
   - .hb
   tm_scope: none
+  ace_mode: none
 
 Haskell:
   type: programming
@@ -1125,6 +1237,7 @@ Haskell:
   extensions:
   - .hs
   - .hsc
+  ace_mode: haskell
 
 Haxe:
   type: programming
@@ -1151,6 +1264,7 @@ IDL:
   extensions:
   - .pro
   - .dlm
+  ace_mode: none
 
 IGOR Pro:
   type: programming
@@ -1160,6 +1274,7 @@ IGOR Pro:
   - igor
   - igorpro
   tm_scope: none
+  ace_mode: none
 
 INI:
   type: data
@@ -1171,6 +1286,7 @@ INI:
   tm_scope: source.ini
   aliases:
   - dosini
+  ace_mode: ini
 
 IRC log:
   search_term: irc
@@ -1181,12 +1297,14 @@ IRC log:
   - .irclog
   - .weechatlog
   tm_scope: none
+  ace_mode: none
 
 Idris:
   type: programming
   extensions:
   - .idr
   - .lidr
+  ace_mode: none
 
 Inform 7:
   type: programming
@@ -1198,17 +1316,20 @@ Inform 7:
   aliases:
   - i7
   - inform7
+  ace_mode: none
 
 Inno Setup:
   extensions:
   - .iss
   tm_scope: none
+  ace_mode: none
 
 Io:
   type: programming
   color: "#a9188d"
   extensions:
   - .io
+  ace_mode: io
 
 Ioke:
   type: programming
@@ -1217,6 +1338,7 @@ Ioke:
   - .ik
   interpreters:
   - ioke
+  ace_mode: none
 
 Isabelle:
   type: programming
@@ -1224,12 +1346,14 @@ Isabelle:
   extensions:
   - .thy
   tm_scope: source.isabelle.theory
+  ace_mode: none
 
 J:
   type: programming
   extensions:
   - .ijs
   tm_scope: none
+  ace_mode: none
 
 JSON:
   type: data
@@ -1256,11 +1380,12 @@ JSON5:
   extensions:
   - .json5
   tm_scope: source.js
+  ace_mode: javascript
 
 JSONLD:
   type: data
   group: JavaScript
-  ace_mode: json
+  ace_mode: javascript
   extensions:
   - .jsonld
   tm_scope: source.js
@@ -1278,6 +1403,7 @@ Jade:
   extensions:
   - .jade
   tm_scope: source.jade
+  ace_mode: jade
 
 Java:
   type: programming
@@ -1294,6 +1420,7 @@ Java Server Pages:
   extensions:
   - .jsp
   tm_scope: text.html.jsp
+  ace_mode: jsp
 
 JavaScript:
   type: programming
@@ -1332,6 +1459,7 @@ Julia:
   extensions:
   - .jl
   color: "#a270ba"
+  ace_mode: julia
 
 KRL:
   type: programming
@@ -1339,6 +1467,7 @@ KRL:
   extensions:
   - .krl
   tm_scope: none
+  ace_mode: none
 
 Kit:
   type: markup
@@ -1354,6 +1483,7 @@ Kotlin:
   - .ktm
   - .kts
   tm_scope: source.Kotlin
+  ace_mode: none
 
 LFE:
   type: programming
@@ -1362,10 +1492,12 @@ LFE:
   color: "#004200"
   group: Erlang
   tm_scope: source.lisp
+  ace_mode: lisp
 
 LLVM:
   extensions:
   - .ll
+  ace_mode: none
 
 LOLCODE:
   type: programming
@@ -1373,6 +1505,7 @@ LOLCODE:
   - .lol
   color: "#cc9900"
   tm_scope: none
+  ace_mode: none
 
 LSL:
   type: programming
@@ -1388,6 +1521,7 @@ LabVIEW:
   extensions:
   - .lvproj
   tm_scope: none
+  ace_mode: none
 
 Lasso:
   type: programming
@@ -1401,6 +1535,7 @@ Lasso:
   tm_scope: file.lasso
   aliases:
   - lassoscript
+  ace_mode: none
 
 Latte:
   type: markup
@@ -1409,6 +1544,7 @@ Latte:
   extensions:
   - .latte
   tm_scope: source.smarty
+  ace_mode: smarty
 
 Less:
   type: markup
@@ -1416,17 +1552,20 @@ Less:
   extensions:
   - .less
   tm_scope: source.css.less
+  ace_mode: less
 
 LilyPond:
   extensions:
   - .ly
   - .ily
+  ace_mode: none
 
 Liquid:
   type: markup
   extensions:
   - .liquid
   tm_scope: none
+  ace_mode: liquid
 
 Literate Agda:
   type: programming
@@ -1434,6 +1573,7 @@ Literate Agda:
   extensions:
   - .lagda
   tm_scope: none
+  ace_mode: none
 
 Literate CoffeeScript:
   type: programming
@@ -1446,6 +1586,7 @@ Literate CoffeeScript:
   - litcoffee
   extensions:
   - .litcoffee
+  ace_mode: none
 
 Literate Haskell:
   type: programming
@@ -1457,10 +1598,10 @@ Literate Haskell:
   extensions:
   - .lhs
   tm_scope: text.tex.latex.haskell
+  ace_mode: none
 
 LiveScript:
   type: programming
-  ace_mode: ls
   color: "#499886"
   aliases:
   - live-script
@@ -1470,6 +1611,7 @@ LiveScript:
   - ._ls
   filenames:
   - Slakefile
+  ace_mode: livescript
 
 Logos:
   type: programming
@@ -1477,12 +1619,14 @@ Logos:
   - .xm
   - .x
   - .xi
+  ace_mode: none
 
 Logtalk:
   type: programming
   extensions:
   - .lgt
   - .logtalk
+  ace_mode: none
 
 LookML:
   type: programming
@@ -1497,6 +1641,7 @@ LoomScript:
   extensions:
   - .ls
   tm_scope: source.loomscript
+  ace_mode: none
 
 Lua:
   type: programming
@@ -1520,6 +1665,7 @@ M:
   - .mumps
   - .m
   tm_scope: source.lisp
+  ace_mode: lisp
 
 MTML:
   type: markup
@@ -1527,6 +1673,7 @@ MTML:
   extensions:
   - .mtml
   tm_scope: text.html.basic
+  ace_mode: html
 
 Makefile:
   type: programming
@@ -1543,12 +1690,14 @@ Makefile:
   - makefile
   interpreters:
   - make
+  ace_mode: makefile
 
 Mako:
   extensions:
   - .mako
   - .mao
   tm_scope: text.html.mako
+  ace_mode: none
 
 Markdown:
   type: prose
@@ -1566,7 +1715,7 @@ Markdown:
 Mask:
   type: markup
   color: "#f97732"
-  ace_mode: scss
+  ace_mode: mask
   extensions:
   - .mask
   tm_scope: source.scss
@@ -1582,6 +1731,7 @@ Mathematica:
   - .nbp
   aliases:
   - mma
+  ace_mode: none
 
 Matlab:
   type: programming
@@ -1589,12 +1739,14 @@ Matlab:
   extensions:
   - .matlab
   - .m
+  ace_mode: matlab
 
 Maven POM:
   type: data
   tm_scope: text.xml.pom
   filenames:
   - pom.xml
+  ace_mode: xml
 
 Max:
   type: programming
@@ -1610,6 +1762,7 @@ Max:
   - .mxt
   - .pat
   tm_scope: source.json
+  ace_mode: json
 
 MediaWiki:
   type: prose
@@ -1617,6 +1770,7 @@ MediaWiki:
   extensions:
   - .mediawiki
   tm_scope: none
+  ace_mode: none
 
 Mercury:
   type: programming
@@ -1628,12 +1782,14 @@ Mercury:
   - .m
   - .moo
   tm_scope: source.prolog
+  ace_mode: prolog
 
 MiniD: # Legacy
   searchable: false
   extensions:
   - .minid # Dummy extension
   tm_scope: none
+  ace_mode: none
 
 Mirah:
   type: programming
@@ -1645,17 +1801,20 @@ Mirah:
   - .mir
   - .mirah
   tm_scope: source.ruby
+  ace_mode: ruby
 
 Monkey:
   type: programming
   extensions:
   - .monkey
+  ace_mode: none
 
 Moocode:
   type: programming
   extensions:
   - .moo
   tm_scope: none
+  ace_mode: none
 
 MoonScript:
   type: programming
@@ -1663,22 +1822,26 @@ MoonScript:
   - .moon
   interpreters:
   - moon
+  ace_mode: none
 
 Myghty:
   extensions:
   - .myt
   tm_scope: none
+  ace_mode: none
 
 NSIS:
   extensions:
   - .nsi
   - .nsh
+  ace_mode: none
 
 Nemerle:
   type: programming
   color: "#0d3c6e"
   extensions:
   - .n
+  ace_mode: none
 
 NetLogo:
   type: programming
@@ -1686,6 +1849,7 @@ NetLogo:
   extensions:
   - .nlogo
   tm_scope: source.lisp
+  ace_mode: lisp
 
 Nginx:
   type: markup
@@ -1694,6 +1858,7 @@ Nginx:
   tm_scope: source.nginx
   aliases:
   - nginx configuration file
+  ace_mode: none
 
 Nimrod:
   type: programming
@@ -1701,12 +1866,14 @@ Nimrod:
   extensions:
   - .nim
   - .nimrod
+  ace_mode: none
 
 Ninja:
   type: data
   tm_scope: source.ninja
   extensions:
   - .ninja
+  ace_mode: none
 
 Nit:
   type: programming
@@ -1714,6 +1881,7 @@ Nit:
   extensions:
   - .nit
   tm_scope: none
+  ace_mode: none
 
 Nix:
   type: programming
@@ -1723,6 +1891,7 @@ Nix:
   aliases:
   - nixos
   tm_scope: source.nix
+  ace_mode: nix
 
 Nu:
   type: programming
@@ -1734,6 +1903,7 @@ Nu:
   filenames:
   - Nukefile
   tm_scope: source.scheme
+  ace_mode: scheme
   interpreters:
   - nush
 
@@ -1744,6 +1914,7 @@ NumPy:
   - .numpyw
   - .numsc
   tm_scope: none
+  ace_mode: none
 
 OCaml:
   type: programming
@@ -1763,6 +1934,7 @@ ObjDump:
   extensions:
   - .objdump
   tm_scope: objdump.x86asm
+  ace_mode: assembly_x86
 
 Objective-C:
   type: programming
@@ -1775,6 +1947,7 @@ Objective-C:
   extensions:
   - .m
   - .h
+  ace_mode: objectivec
 
 Objective-C++:
   type: programming
@@ -1786,6 +1959,7 @@ Objective-C++:
   - objectivec++
   extensions:
   - .mm
+  ace_mode: objectivec
 
 Objective-J:
   type: programming
@@ -1798,6 +1972,7 @@ Objective-J:
   - .j
   - .sj
   tm_scope: source.js.objj
+  ace_mode: none
 
 Omgrofl:
   type: programming
@@ -1805,11 +1980,13 @@ Omgrofl:
   - .omgrofl
   color: "#cabbff"
   tm_scope: none
+  ace_mode: none
 
 Opa:
   type: programming
   extensions:
   - .opa
+  ace_mode: none
 
 Opal:
   type: programming
@@ -1817,6 +1994,7 @@ Opal:
   extensions:
   - .opal
   tm_scope: none
+  ace_mode: none
 
 OpenCL:
   type: programming
@@ -1825,6 +2003,7 @@ OpenCL:
   - .cl
   - .opencl
   tm_scope: source.c
+  ace_mode: c_cpp
 
 OpenEdge ABL:
   type: programming
@@ -1836,12 +2015,14 @@ OpenEdge ABL:
   - .p
   - .cls
   tm_scope: source.abl
+  ace_mode: none
 
 OpenSCAD:
   type: programming
   extensions:
   - .scad
   tm_scope: none
+  ace_mode: none
 
 Org:
   type: prose
@@ -1849,6 +2030,7 @@ Org:
   extensions:
   - .org
   tm_scope: none
+  ace_mode: none
 
 Ox:
   type: programming
@@ -1857,6 +2039,7 @@ Ox:
   - .oxh
   - .oxo
   tm_scope: none
+  ace_mode: none
 
 Oxygene:
   type: programming
@@ -1864,6 +2047,7 @@ Oxygene:
   extensions:
   - .oxygene
   tm_scope: none
+  ace_mode: none
 
 Oz:
   type: programming
@@ -1871,6 +2055,7 @@ Oz:
   extensions:
   - .oz
   tm_scope: source.oz
+  ace_mode: none
 
 PAWN:
   type: programming
@@ -1878,6 +2063,7 @@ PAWN:
   extensions:
   - .pwn
   tm_scope: source.c++
+  ace_mode: c_cpp
 
 PHP:
   type: programming
@@ -1906,6 +2092,7 @@ Pan:
   extensions:
   - .pan
   tm_scope: none
+  ace_mode: none
 
 Papyrus:
   type: programming
@@ -1913,6 +2100,7 @@ Papyrus:
   extensions:
   - .psc
   tm_scope: none
+  ace_mode: none
 
 Parrot:
   type: programming
@@ -1920,6 +2108,7 @@ Parrot:
   extensions:
   - .parrot # Dummy extension
   tm_scope: none
+  ace_mode: none
 
 Parrot Assembly:
   group: Parrot
@@ -1931,6 +2120,7 @@ Parrot Assembly:
   interpreters:
   - parrot
   tm_scope: none
+  ace_mode: none
 
 Parrot Internal Representation:
   group: Parrot
@@ -1942,6 +2132,7 @@ Parrot Internal Representation:
   - .pir
   interpreters:
   - parrot
+  ace_mode: none
 
 Pascal:
   type: programming
@@ -1952,6 +2143,7 @@ Pascal:
   - .dpr
   - .lpr
   - .pp
+  ace_mode: pascal
 
 Perl:
   type: programming
@@ -1990,6 +2182,7 @@ Perl6:
   interpreters:
   - perl6
   tm_scope: none
+  ace_mode: perl
 
 PigLatin:
   type: programming
@@ -1997,6 +2190,7 @@ PigLatin:
   extensions:
   - .pig
   tm_scope: none
+  ace_mode: none
 
 Pike:
   type: programming
@@ -2004,6 +2198,7 @@ Pike:
   extensions:
   - .pike
   - .pmod
+  ace_mode: none
 
 Pod:
   type: prose
@@ -2019,6 +2214,7 @@ PogoScript:
   extensions:
   - .pogo
   tm_scope: none
+  ace_mode: none
 
 PostScript:
   type: markup
@@ -2028,6 +2224,7 @@ PostScript:
   tm_scope: source.postscript
   aliases:
   - postscr
+  ace_mode: none
 
 PowerShell:
   type: programming
@@ -2044,6 +2241,7 @@ Processing:
   color: "#2779ab"
   extensions:
   - .pde
+  ace_mode: none
 
 Prolog:
   type: programming
@@ -2055,6 +2253,7 @@ Prolog:
   - .prolog
   interpreters:
   - swipl
+  ace_mode: prolog
 
 Propeller Spin:
   type: programming
@@ -2062,6 +2261,7 @@ Propeller Spin:
   extensions:
   - .spin
   tm_scope: none
+  ace_mode: none
 
 Protocol Buffer:
   type: markup
@@ -2071,6 +2271,7 @@ Protocol Buffer:
   extensions:
   - .proto
   tm_scope: source.protobuf
+  ace_mode: protobuf
 
 Puppet:
   type: programming
@@ -2079,6 +2280,7 @@ Puppet:
   - .pp
   filenames:
   - Modulefile
+  ace_mode: none
 
 Pure Data:
   type: programming
@@ -2086,6 +2288,7 @@ Pure Data:
   extensions:
   - .pd
   tm_scope: none
+  ace_mode: none
 
 PureScript:
   type: programming
@@ -2093,6 +2296,7 @@ PureScript:
   extensions:
   - .purs
   tm_scope: source.haskell
+  ace_mode: haskell
 
 Python:
   type: programming
@@ -2128,6 +2332,7 @@ Python traceback:
   extensions:
   - .pytb
   tm_scope: text.python.traceback
+  ace_mode: none
 
 QML:
   type: markup
@@ -2135,6 +2340,7 @@ QML:
   extensions:
   - .qml
   tm_scope: source.qml
+  ace_mode: none
 
 QMake:
   extensions:
@@ -2142,6 +2348,7 @@ QMake:
   - .pri
   interpreters:
   - qmake
+  ace_mode: none
 
 R:
   type: programming
@@ -2160,6 +2367,7 @@ R:
   - .Rprofile
   interpreters:
   - Rscript
+  ace_mode: r
 
 RAML:
   type: data
@@ -2188,6 +2396,7 @@ REALbasic:
   - .rbtbar
   - .rbuistate
   tm_scope: source.vbnet
+  ace_mode: none
 
 RHTML:
   type: markup
@@ -2197,6 +2406,7 @@ RHTML:
   tm_scope: text.html.erb
   aliases:
   - html+ruby
+  ace_mode: rhtml
 
 RMarkdown:
   type: prose
@@ -2216,6 +2426,7 @@ Racket:
   - .rktl
   - .scrbl
   tm_scope: source.racket
+  ace_mode: lisp
 
 Ragel in Ruby Host:
   type: programming
@@ -2226,6 +2437,7 @@ Ragel in Ruby Host:
   - ragel-rb
   - ragel-ruby
   tm_scope: none
+  ace_mode: none
 
 Raw token data:
   search_term: raw
@@ -2234,6 +2446,7 @@ Raw token data:
   extensions:
   - .raw
   tm_scope: none
+  ace_mode: none
 
 Rebol:
   type: programming
@@ -2244,6 +2457,7 @@ Rebol:
   - .r2
   - .r3
   - .rebol
+  ace_mode: none
 
 Red:
   type: programming
@@ -2254,11 +2468,13 @@ Red:
   aliases:
   - red/system
   tm_scope: none
+  ace_mode: none
 
 Redcode:
   extensions:
   - .cw
   tm_scope: none
+  ace_mode: none
 
 RobotFramework:
   type: programming
@@ -2266,6 +2482,7 @@ RobotFramework:
   - .robot
   # - .txt
   tm_scope: text.robot
+  ace_mode: none
 
 Rouge:
   type: programming
@@ -2328,6 +2545,7 @@ Rust:
   color: "#dea584"
   extensions:
   - .rs
+  ace_mode: rust
 
 SAS:
   type: programming
@@ -2335,6 +2553,7 @@ SAS:
   extensions:
   - .sas
   tm_scope: none
+  ace_mode: none
 
 SCSS:
   type: markup
@@ -2351,6 +2570,7 @@ SQF:
   - .sqf
   - .hqf
   tm_scope: source.sqf
+  ace_mode: none
 
 SQL:
   type: data
@@ -2369,6 +2589,7 @@ STON:
   extensions:
   - .ston
   tm_scope: source.json
+  ace_mode: lisp
 
 Sage:
   type: programming
@@ -2376,6 +2597,7 @@ Sage:
   extensions:
   - .sage
   tm_scope: source.python
+  ace_mode: python
 
 SaltStack:
   type: data
@@ -2393,6 +2615,7 @@ Sass:
   group: CSS
   extensions:
   - .sass
+  ace_mode: sass
 
 Scala:
   type: programming
@@ -2411,6 +2634,7 @@ Scaml:
   extensions:
   - .scaml
   tm_scope: source.scaml
+  ace_mode: none
 
 Scheme:
   type: programming
@@ -2426,6 +2650,7 @@ Scheme:
   - racket
   - bigloo
   - chicken
+  ace_mode: scheme
 
 Scilab:
   type: programming
@@ -2433,6 +2658,7 @@ Scilab:
   - .sci
   - .sce
   - .tst
+  ace_mode: none
 
 Self:
   type: programming
@@ -2440,6 +2666,7 @@ Self:
   extensions:
   - .self
   tm_scope: none
+  ace_mode: none
 
 Shell:
   type: programming
@@ -2463,6 +2690,7 @@ Shell:
   - bash
   - sh
   - zsh
+  ace_mode: sh
 
 ShellSession:
   type: programming
@@ -2472,6 +2700,7 @@ ShellSession:
   - bash session
   - console
   tm_scope: text.shell-session
+  ace_mode: sh
 
 Shen:
   type: programming
@@ -2479,6 +2708,7 @@ Shen:
   extensions:
   - .shen
   tm_scope: none
+  ace_mode: none
 
 Slash:
   type: programming
@@ -2486,6 +2716,7 @@ Slash:
   extensions:
   - .sl
   tm_scope: text.html.slash
+  ace_mode: none
 
 Slim:
   group: HTML
@@ -2493,6 +2724,7 @@ Slim:
   color: "#ff8877"
   extensions:
   - .slim
+  ace_mode: none
 
 Smalltalk:
   type: programming
@@ -2501,10 +2733,12 @@ Smalltalk:
   - .st
   aliases:
   - squeak
+  ace_mode: none
 
 Smarty:
   extensions:
   - .tpl
+  ace_mode: smarty
 
 SourcePawn:
   type: programming
@@ -2514,12 +2748,14 @@ SourcePawn:
   extensions:
   - .sp
   tm_scope: source.sp
+  ace_mode: none
 
 Squirrel:
   type: programming
   extensions:
   - .nut
   tm_scope: source.c++
+  ace_mode: c_cpp
 
 Standard ML:
   type: programming
@@ -2532,6 +2768,7 @@ Standard ML:
   - .sig
   - .sml
   tm_scope: source.ml
+  ace_mode: none
 
 Stata:
   type: programming
@@ -2543,6 +2780,7 @@ Stata:
   - .mata
   - .matah
   - .sthlp
+  ace_mode: none
 
 Stylus:
   type: markup
@@ -2550,6 +2788,7 @@ Stylus:
   extensions:
   - .styl
   tm_scope: none
+  ace_mode: stylus
 
 SuperCollider:
   type: programming
@@ -2558,12 +2797,14 @@ SuperCollider:
   - .scd
   - .sc
   tm_scope: none
+  ace_mode: none
 
 Swift:
   type: programming
   color: "#ffac45"
   extensions:
   - .swift
+  ace_mode: none
 
 SystemVerilog:
   type: programming
@@ -2572,18 +2813,21 @@ SystemVerilog:
   - .sv
   - .svh
   - .vh
+  ace_mode: verilog
 
 TOML:
   type: data
   extensions:
   - .toml
   tm_scope: source.toml
+  ace_mode: toml
 
 TXL:
   type: programming
   extensions:
   - .txl
   tm_scope: none
+  ace_mode: none
 
 Tcl:
   type: programming
@@ -2595,6 +2839,7 @@ Tcl:
   interpreters:
   - tclsh
   - wish
+  ace_mode: tcl
 
 Tcsh:
   type: programming
@@ -2603,11 +2848,12 @@ Tcsh:
   - .tcsh
   - .csh
   tm_scope: source.shell
+  ace_mode: sh
 
 TeX:
   type: markup
   color: "#3D6117"
-  ace_mode: latex
+  ace_mode: tex
   wrap: true
   aliases:
   - latex
@@ -2633,6 +2879,7 @@ Tea:
   extensions:
   - .tea
   tm_scope: source.tea
+  ace_mode: none
 
 Textile:
   type: prose
@@ -2647,6 +2894,7 @@ Thrift:
   tm_scope: source.thrift
   extensions:
   - .thrift
+  ace_mode: none
 
 Turing:
   type: programming
@@ -2655,6 +2903,7 @@ Turing:
   - .t
   - .tu
   tm_scope: none
+  ace_mode: none
 
 Twig:
   type: markup
@@ -2662,6 +2911,7 @@ Twig:
   extensions:
   - .twig
   tm_scope: text.html.twig
+  ace_mode: twig
 
 TypeScript:
   type: programming
@@ -2671,6 +2921,7 @@ TypeScript:
   extensions:
   - .ts
   tm_scope: source.ts
+  ace_mode: typescript
 
 Unified Parallel C:
   type: programming
@@ -2687,6 +2938,7 @@ UnrealScript:
   extensions:
   - .uc
   tm_scope: source.java
+  ace_mode: java
 
 VCL:
   type: programming
@@ -2708,6 +2960,7 @@ VHDL:
   - .vhs
   - .vht
   - .vhw
+  ace_mode: vhdl
 
 Vala:
   type: programming
@@ -2715,6 +2968,7 @@ Vala:
   extensions:
   - .vala
   - .vapi
+  ace_mode: vala
 
 Verilog:
   type: programming
@@ -2722,6 +2976,7 @@ Verilog:
   extensions:
   - .v
   - .veo
+  ace_mode: verilog
 
 VimL:
   type: programming
@@ -2736,6 +2991,7 @@ VimL:
   - _vimrc
   - gvimrc
   - vimrc
+  ace_mode: none
 
 Visual Basic:
   type: programming
@@ -2753,6 +3009,7 @@ Visual Basic:
   aliases:
   - vb.net
   - vbnet
+  ace_mode: none
 
 Volt:
   type: programming
@@ -2760,12 +3017,14 @@ Volt:
   extensions:
   - .volt
   tm_scope: source.d
+  ace_mode: d
 
 XC:
   type: programming
   extensions:
   - .xc
   tm_scope: source.c
+  ace_mode: c_cpp
 
 XML:
   type: markup
@@ -2851,6 +3110,7 @@ XProc:
   - .xpl
   - .xproc
   tm_scope: text.xml
+  ace_mode: xml
 
 XQuery:
   type: programming
@@ -2861,11 +3121,13 @@ XQuery:
   - .xql
   - .xqm
   - .xqy
+  ace_mode: xquery
 
 XS:
   extensions:
   - .xs
   tm_scope: source.c
+  ace_mode: c_cpp
 
 XSLT:
   type: programming
@@ -2875,6 +3137,7 @@ XSLT:
   - .xslt
   - .xsl
   tm_scope: text.xml.xsl
+  ace_mode: xml
 
 Xojo:
   type: programming
@@ -2886,11 +3149,13 @@ Xojo:
   - .xojo_toolbar
   - .xojo_window
   tm_scope: source.vbnet
+  ace_mode: none
 
 Xtend:
   type: programming
   extensions:
   - .xtend
+  ace_mode: none
 
 YAML:
   type: data
@@ -2902,6 +3167,7 @@ YAML:
   - .reek
   - .rviz
   - .yaml
+  ace_mode: yaml
 
 Zephir:
   type: programming
@@ -2909,6 +3175,7 @@ Zephir:
   extensions:
   - .zep
   tm_scope: source.php.zephir
+  ace_mode: php
 
 Zimpl:
   type: programming
@@ -2917,6 +3184,7 @@ Zimpl:
   - .zmpl
   - .zpl
   tm_scope: none
+  ace_mode: none
 
 eC:
   type: programming
@@ -2925,6 +3193,7 @@ eC:
   - .ec
   - .eh
   tm_scope: none
+  ace_mode: none
 
 edn:
   type: data
@@ -2940,22 +3209,26 @@ fish:
   extensions:
   - .fish
   tm_scope: none
+  ace_mode: none
 
 mupad:
   extensions:
   - .mu
+  ace_mode: none
 
 nesC:
   type: programming
   color: "#ffce3b"
   extensions:
   - .nc
+  ace_mode: none
 
 ooc:
   type: programming
   color: "#b0b77e"
   extensions:
   - .ooc
+  ace_mode: none
 
 reStructuredText:
   type: prose
@@ -2966,6 +3239,7 @@ reStructuredText:
   extensions:
   - .rst
   - .rest
+  ace_mode: none
 
 wisp:
   type: programming
@@ -2981,3 +3255,4 @@ xBase:
   extensions:
   - .prg
   tm_scope: none
+  ace_mode: none
diff --git a/test/test_blob.rb b/test/test_blob.rb
index b59fbec7..12ea1338 100644
--- a/test/test_blob.rb
+++ b/test/test_blob.rb
@@ -469,7 +469,7 @@ class TestBlob < Test::Unit::TestCase
     # Test language detection for files which shouldn't be used as samples
     root = File.expand_path('../fixtures', __FILE__)
     Dir.entries(root).each do |language|
-      next if language == '.' || language == '..'
+      next if language == '.' || language == '..' || File.basename(language) == 'ace_modes.json'
 
       # Each directory contains test files of a language
       dirname = File.join(root, language)
diff --git a/test/test_language.rb b/test/test_language.rb
index 9a7498d1..2bfec9fa 100644
--- a/test/test_language.rb
+++ b/test/test_language.rb
@@ -308,11 +308,11 @@ class TestLanguage < Test::Unit::TestCase
     assert_equal 'css', Language['CSS'].ace_mode
     assert_equal 'lsl', Language['LSL'].ace_mode
     assert_equal 'javascript', Language['JavaScript'].ace_mode
+    assert_equal 'none', Language['FORTRAN'].ace_mode
   end
 
   def test_ace_modes
     assert Language.ace_modes.include?(Language['Ruby'])
-    assert !Language.ace_modes.include?(Language['FORTRAN'])
   end
 
   def test_wrap
@@ -356,4 +356,22 @@ class TestLanguage < Test::Unit::TestCase
     message << missing.map { |language| sprintf("%-#{width}s %s", language.name, language.tm_scope) }.sort.join("\n")
     assert missing.empty?, message
   end
+
+  def test_all_languages_have_a_valid_ace_mode
+    ace_fixture_path = File.join('test', 'fixtures', 'ace_modes.json')
+    skip("No ace_modes.json file") unless File.exist?(ace_fixture_path)
+
+    ace_github_modes = Yajl.load(File.read(ace_fixture_path))
+    existing_ace_modes = ace_github_modes.map do |ace_github_mode|
+      File.basename(ace_github_mode["name"], ".js") if ace_github_mode["name"]  !~ /_highlight_rules|_test|_worker/
+    end.compact.uniq.sort.map(&:downcase)
+
+    missing = Language.all.reject { |language| language.ace_mode == "none" || existing_ace_modes.include?(language.ace_mode) }
+    message = "The following languages do not have an Ace mode listed in languages.yml. Please add an Ace mode for all new languages.\n"
+    message << "If no Ace mode exists for a language, mark the language with `ace_mode: none` in lib/linguist/languages.yml.\n"
+
+    width = missing.map { |language| language.name.length }.max
+    message << missing.map { |language| sprintf("%-#{width}s %s", language.name, language.ace_mode) }.sort.join("\n")
+    assert missing.empty?, message
+  end
 end