diff --git a/lib/linguist/language.rb b/lib/linguist/language.rb
index 5aa1db8c..3f90900f 100644
--- a/lib/linguist/language.rb
+++ b/lib/linguist/language.rb
@@ -206,8 +206,12 @@ module Linguist
     #   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
 
diff --git a/test/test_language.rb b/test/test_language.rb
index 066f577a..0c7adf81 100644
--- a/test/test_language.rb
+++ b/test/test_language.rb
@@ -243,8 +243,8 @@ class TestLanguage < Test::Unit::TestCase
 
   def test_find_by_extension
     assert_equal [], Language.find_by_extension('.factor-rc')
-    assert_equal [], Language.find_by_extension('rb')
     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