diff --git a/src/Handler/Utils/Form.hs b/src/Handler/Utils/Form.hs
index 989887b4a..ed8395922 100644
--- a/src/Handler/Utils/Form.hs
+++ b/src/Handler/Utils/Form.hs
@@ -929,8 +929,11 @@ genericFileField mkOpts = Field{..}
         handleFile
           | doUnpack  = sourceFiles
           | otherwise = yieldM . acceptFile
+        invalidUploadExtension fName
+          = not (permittedExtension opts fName)
+         && (not doUnpack || ((/=) `on` simpleContentType) (mimeLookup fName) typeZip)
 
-      if | invExt : _ <- filter (not . permittedExtension opts) uploadedFilenames
+      if | invExt : _ <- filter invalidUploadExtension uploadedFilenames
            -> do
              liftHandler . runDB . runConduit $
                   mapM_ (transPipe lift . handleFile) files