diff --git a/lib/rouge/lexers/docker.rb b/lib/rouge/lexers/docker.rb
index a2e31bd043..a079997016 100644
--- a/lib/rouge/lexers/docker.rb
+++ b/lib/rouge/lexers/docker.rb
@@ -8,7 +8,7 @@ class Docker < RegexLexer
       desc "Dockerfile syntax"
       tag 'docker'
       aliases 'dockerfile'
-      filenames 'Dockerfile', '*.Dockerfile', '*.docker', 'Dockerfile_*'
+      filenames 'Dockerfile', '*.Dockerfile', '*.docker'
       mimetypes 'text/x-dockerfile-config'
 
       KEYWORDS = %w(
diff --git a/spec/lexers/docker_spec.rb b/spec/lexers/docker_spec.rb
index a1f4480d5e..64e48c4dff 100644
--- a/spec/lexers/docker_spec.rb
+++ b/spec/lexers/docker_spec.rb
@@ -11,7 +11,6 @@
       assert_guess :filename => 'Dockerfile'
       assert_guess :filename => 'docker.docker'
       assert_guess :filename => 'some.Dockerfile'
-      assert_guess :filename => 'Dockerfile_some_extension'
     end
 
     it 'guesses by mimetype' do