diff --git a/lib/linguist/heuristics.rb b/lib/linguist/heuristics.rb
index b82a5de4..bc9a0f53 100644
--- a/lib/linguist/heuristics.rb
+++ b/lib/linguist/heuristics.rb
@@ -178,11 +178,13 @@ module Linguist
       end
     end
 
-    disambiguate "M", "Mathematica", "Matlab", "Mercury", "Objective-C" do |data|
+    disambiguate "M", "MUF", "Mathematica", "Matlab", "Mercury", "Objective-C" do |data|
       if ObjectiveCRegex.match(data)
         Language["Objective-C"]
       elsif data.include?(":- module")
         Language["Mercury"]
+      elsif /^: /.match(data)
+        Language["MUF"]
       elsif /^\s*;/.match(data)
         Language["M"]
       elsif /^\s*\(\*/.match(data)
diff --git a/lib/linguist/languages.yml b/lib/linguist/languages.yml
index 413683e5..2f96958c 100644
--- a/lib/linguist/languages.yml
+++ b/lib/linguist/languages.yml
@@ -1745,6 +1745,15 @@ MTML:
   tm_scope: text.html.basic
   ace_mode: html
 
+MUF:
+  type: programming
+  group: Forth
+  extensions:
+  - .muf
+  - .m
+  tm_scope: none
+  ace_mode: forth
+
 Makefile:
   type: programming
   aliases:
diff --git a/test/test_language.rb b/test/test_language.rb
index 31be9a82..f3847a77 100644
--- a/test/test_language.rb
+++ b/test/test_language.rb
@@ -188,7 +188,7 @@ class TestLanguage < Minitest::Test
     assert_equal [], Language.find_by_extension('foo.rb')
     assert_equal [Language['Ruby']], Language.find_by_extension('rb')
     assert_equal [Language['Ruby']], Language.find_by_extension('.rb')
-    assert_equal [Language['M'], Language['Mathematica'], Language['Matlab'], Language['Mercury'], Language['Objective-C']], Language.find_by_extension('.m')
+    assert_equal [Language['M'], Language['MUF'], Language['Mathematica'], Language['Matlab'], Language['Mercury'], Language['Objective-C']], Language.find_by_extension('.m')
   end
 
   def test_find_all_by_extension