@@ -242,7 +242,12 @@ exportType
242242 -> m Exports
243243exportType exportMode exps name dctors mn = do
244244 let exTypes = exportedTypes exps
245− let exClasses = exportedTypeClasses exps
245+ exClasses = exportedTypeClasses exps
246+ dctorNameCounts :: [(ProperName 'ConstructorName, Int)]
247+ dctorNameCounts = M.toList $ M.fromListWith (+) (map (,1) dctors)
248+ forM_ dctorNameCounts $ \(dctorName, count) ->
249+ when (count > 1) $
250+ throwDeclConflict (DctorName dctorName) (DctorName dctorName)
246251 case exportMode of
247252 Internal -> do
248253 when (name `M.member` exTypes) $