diff --git a/lib/linguist/language.rb b/lib/linguist/language.rb
index 49c10bf7..4dd06bb4 100644
--- a/lib/linguist/language.rb
+++ b/lib/linguist/language.rb
@@ -194,9 +194,25 @@ module Linguist
     def self.find_by_filename(filename)
       basename = File.basename(filename)
       extname = FileBlob.new(filename).extension
-      langs = @filename_index[basename] +
-              @extension_index[extname]
-      langs.compact.uniq
+      (@filename_index[basename] + find_by_extension(extname)).compact.uniq
+    end
+
+    # Public: Look up Languages by file extension.
+    #
+    # extname - The extension String.
+    #
+    # Examples
+    #
+    #   Language.find_by_extension('.rb')
+    #   # => [#<Language name="Ruby">]
+    #
+    #   Language.find_by_extension('rb')
+    #   # => [#<Language name="Ruby">]
+    #
+    # Returns all matching Languages or [] if none were found.
+    def self.find_by_extension(extname)
+      extname = ".#{extname}" unless extname.start_with?(".")
+      @extension_index[extname]
     end
 
     # Public: Look up Languages by shebang line.
diff --git a/test/test_language.rb b/test/test_language.rb
index 0039dc2b..77f5ecba 100644
--- a/test/test_language.rb
+++ b/test/test_language.rb
@@ -241,6 +241,22 @@ class TestLanguage < Test::Unit::TestCase
     end
   end
 
+  def test_find_by_extension
+    assert_equal [], Language.find_by_extension('.factor-rc')
+    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')
+  end
+
+  def test_find_all_by_extension
+    Language.all.each do |language|
+      language.extensions.each do |extension|
+        assert_include Language.find_by_extension(extension), language
+      end
+    end
+  end
+
   def test_find_by_filename
     assert_equal [Language['Shell']], Language.find_by_filename('PKGBUILD')
     assert_equal [Language['Ruby']], Language.find_by_filename('foo.rb')