diff --git a/lib/linguist/blob_helper.rb b/lib/linguist/blob_helper.rb
index 5f843ac6..44264327 100644
--- a/lib/linguist/blob_helper.rb
+++ b/lib/linguist/blob_helper.rb
@@ -281,6 +281,9 @@ module Linguist
         # If it's a .m file, try to guess the language
         m_language ||
 
+        # If it's a .pl file, try to guess the language
+        pl_language ||
+
         # If it's a .r file, try to guess the language
         r_language ||
 
@@ -347,6 +350,26 @@ module Linguist
       end
     end
 
+    # Internal: Guess language of .pl files
+    #
+    # Returns a Language.
+    def pl_language
+      return unless extname == '.pl'
+
+      # The rules for disambiguation are:
+      #
+      # 1. Many perl files begin with a shebang
+      # 2. Most Prolog source files have a rule somewhere (marked by the :- operator)
+      # 3. Default to Perl, because it is more popular
+      if shebang_script == 'perl'
+        Language['Perl']
+      elsif lines.grep(/:-/).any?
+        Language['Prolog']
+      else
+        Language['Perl']
+      end
+    end
+
     # Internal: Guess language of .r files.
     #
     # Returns a Language.
diff --git a/lib/linguist/languages.yml b/lib/linguist/languages.yml
index f36ee009..ffae58e5 100644
--- a/lib/linguist/languages.yml
+++ b/lib/linguist/languages.yml
@@ -590,6 +590,12 @@ Perl:
   - .perl
   - .psgi
 
+Prolog:
+  major: true
+  extensions:
+  - .pro
+  - .prolog
+
 Pure Data:
   major: true
   lexer: Text only
diff --git a/test/fixtures/test-perl.pl b/test/fixtures/test-perl.pl
new file mode 100644
index 00000000..83710279
--- /dev/null
+++ b/test/fixtures/test-perl.pl
@@ -0,0 +1,2 @@
+#!/usr/bin/perl
+print "Hello, world!\n";
diff --git a/test/fixtures/test-perl2.pl b/test/fixtures/test-perl2.pl
new file mode 100644
index 00000000..55a2762c
--- /dev/null
+++ b/test/fixtures/test-perl2.pl
@@ -0,0 +1,3 @@
+
+# Perl file without shebang
+print "Hello, world!\n";
diff --git a/test/fixtures/test-prolog.pl b/test/fixtures/test-prolog.pl
new file mode 100644
index 00000000..aab83d54
--- /dev/null
+++ b/test/fixtures/test-prolog.pl
@@ -0,0 +1,12 @@
+/* Prolog test file */
+male(john).
+male(peter).
+
+female(vick).
+female(christie).
+
+parents(john, peter, christie).
+parents(vick, peter, christie).
+
+/* X is a brother of Y */
+brother(X, Y) :- male(X), parents(X, F, M), parents(Y, F, M).
diff --git a/test/test_blob.rb b/test/test_blob.rb
index 11be67a9..b9b67244 100644
--- a/test/test_blob.rb
+++ b/test/test_blob.rb
@@ -230,9 +230,10 @@ class TestBlob < Test::Unit::TestCase
     assert_equal Language['Ruby'],        blob("wrong_shebang.rb").language
     assert_nil blob("octocat.png").language
 
-    # .r disambiguation
-    assert_equal Language['R'],           blob("hello-r.R").language
-    assert_equal Language['Rebol'],       blob("hello-rebol.r").language
+    # .pl disambiguation
+    assert_equal Language['Prolog'],      blob("test-prolog.pl").language
+    assert_equal Language['Perl'],        blob("test-perl.pl").language
+    assert_equal Language['Perl'],        blob("test-perl2.pl").language
 
     # .m disambiguation
     assert_equal Language['Objective-C'], blob("Foo.m").language
@@ -240,6 +241,10 @@ class TestBlob < Test::Unit::TestCase
     assert_equal Language['Matlab'], blob("matlab_function.m").language
     assert_equal Language['Matlab'], blob("matlab_script.m").language
 
+    # .r disambiguation
+    assert_equal Language['R'],           blob("hello-r.R").language
+    assert_equal Language['Rebol'],       blob("hello-rebol.r").language
+
     # ML
     assert_equal Language['OCaml'],       blob("Foo.ml").language
     assert_equal Language['Standard ML'], blob("Foo.sig").language
diff --git a/test/test_language.rb b/test/test_language.rb
index ffea3054..1a9f4108 100644
--- a/test/test_language.rb
+++ b/test/test_language.rb
@@ -81,6 +81,7 @@ class TestLanguage < Test::Unit::TestCase
     assert_equal Lexer['Ooc'], Language['ooc'].lexer
     assert_equal Lexer['PHP'], Language['PHP'].lexer
     assert_equal Lexer['Perl'], Language['Perl'].lexer
+    assert_equal Lexer['Prolog'], Language['Prolog'].lexer
     assert_equal Lexer['Python Traceback'], Language['Python traceback'].lexer
     assert_equal Lexer['Python'], Language['Python'].lexer
     assert_equal Lexer['REBOL'], Language['Rebol'].lexer
@@ -310,6 +311,7 @@ class TestLanguage < Test::Unit::TestCase
     assert Language['Objective-J'].major?
     assert Language['PHP'].major?
     assert Language['Perl'].major?
+    assert Language['Prolog'].major?
     assert Language['Pure Data'].major?
     assert Language['Python'].major?
     assert Language['R'].major?