diff --git a/lib/dragonfly/app.rb b/lib/dragonfly/app.rb
index <HASH>..<HASH> 100644
--- a/lib/dragonfly/app.rb
+++ b/lib/dragonfly/app.rb
@@ -206,6 +206,7 @@ module Dragonfly
     end
 
     def ext_for(mime_type)
+      return 'txt' if mime_type == 'text/plain'
       ext = mime_types.key(mime_type)
       ext.tr('.', '') if ext
     end
diff --git a/spec/dragonfly/app_spec.rb b/spec/dragonfly/app_spec.rb
index <HASH>..<HASH> 100644
--- a/spec/dragonfly/app_spec.rb
+++ b/spec/dragonfly/app_spec.rb
@@ -95,6 +95,10 @@ describe Dragonfly::App do
       it "returns nil if non-existent" do
         app.ext_for('big/bum').should be_nil
       end
+
+      it "returns txt for text/plain" do
+        app.ext_for('text/plain').should == 'txt'
+      end
     end
   end
an exception for text/plain in App#ext_for