1 files changed, 8 insertions, 6 deletions
diff --git a/compiler/GHC/Core/TyCon.hs b/compiler/GHC/Core/TyCon.hs
index 198b66959b..a038fd646c 100644
--- a/compiler/GHC/Core/TyCon.hs
+++ b/compiler/GHC/Core/TyCon.hs
@@ -2327,12 +2327,14 @@ expandSynTyCon_maybe
 -- ^ Expand a type synonym application, if any
 expandSynTyCon_maybe tc tys
   | SynonymTyCon { tyConTyVars = tvs, synTcRhs = rhs, tyConArity = arity } <- tc
-  = case tys `listLengthCmp` arity of
-        GT -> Just (tvs `zip` tys, rhs, drop arity tys)
-        EQ -> Just (tvs `zip` tys, rhs, [])
-        LT -> Nothing
-  | otherwise
-  = Nothing
+  = case tys of
+      [] -> Just ([], rhs, []) -- Avoid a bit of work in the case of nullary synonyms
+      _  -> case tys `listLengthCmp` arity of
+              GT -> Just (tvs `zip` tys, rhs, drop arity tys)
+              EQ -> Just (tvs `zip` tys, rhs, [])
+              LT -> Nothing
+   | otherwise
+   = Nothing
 
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