diff --git a/Trace/Hpc/Util.hs b/Trace/Hpc/Util.hs
index 5bfbab95fb031acbd0d237cc62632b85056dfd52..ae88aca5b0ae83ee15fc06823a06f76c355450e5 100644
--- a/Trace/Hpc/Util.hs
+++ b/Trace/Hpc/Util.hs
@@ -101,7 +101,7 @@ instance HpcHash a => HpcHash [a] where
   toHash xs = foldl' (\ h c -> toHash c `hxor` (h * 33)) 5381 xs
 
 instance (HpcHash a,HpcHash b) => HpcHash (a,b) where
-  toHash (a,b) = toHash a * 33 `hxor` toHash b
+  toHash (a,b) = (toHash a * 33) `hxor` toHash b
 
 instance HpcHash HpcPos where
   toHash (P a b c d) = Hash $ fromIntegral $ a * 0x1000000 + b * 0x10000 + c * 0x100 + d