diff --git a/compiler/coreSyn/CoreLint.hs b/compiler/coreSyn/CoreLint.hs
index 8c85685d29e8f773d7a50a9ff02456e7db7a848c..2210716fd5fa10437a38edb4e0033c9442e501f9 100644
--- a/compiler/coreSyn/CoreLint.hs
+++ b/compiler/coreSyn/CoreLint.hs
@@ -2080,7 +2080,7 @@ defaultLintFlags = LF { lf_check_global_ids = False
 newtype LintM a =
    LintM { unLintM ::
             LintEnv ->
-            WarnsAndErrs ->           -- Error and warning messages so far
+            WarnsAndErrs ->           -- Warning and error messages so far
             (Maybe a, WarnsAndErrs) } -- Result and messages (if any)
 
 type WarnsAndErrs = (Bag MsgDoc, Bag MsgDoc)
@@ -2189,10 +2189,13 @@ data LintLocInfo
   | InCo   Coercion     -- Inside a coercion
 
 initL :: DynFlags -> LintFlags -> InScopeSet
-       -> LintM a -> WarnsAndErrs    -- Errors and warnings
+       -> LintM a -> WarnsAndErrs    -- Warnings and errors
 initL dflags flags in_scope m
   = case unLintM m env (emptyBag, emptyBag) of
-      (_, errs) -> errs
+      (Just _, errs) -> errs
+      (Nothing, errs@(_, e)) | not (isEmptyBag e) -> errs
+                             | otherwise -> pprPanic ("Bug in Lint: a failure occurred " ++
+                                                      "without reporting an error message") empty
   where
     env = LE { le_flags = flags
              , le_subst = mkEmptyTCvSubst in_scope