diff --git a/lib/data/HappyTemplate.hs b/lib/data/HappyTemplate.hs
index e9e31422..aa8e33a7 100644
--- a/lib/data/HappyTemplate.hs
+++ b/lib/data/HappyTemplate.hs
@@ -251,7 +251,7 @@ happyFail explist i tk action sts stk =
 -- Internal happy errors:
 
 notHappyAtAll :: a
-notHappyAtAll = Prelude.error "Internal Happy error\n"
+notHappyAtAll = Prelude.error "Internal Happy parser panic. This is not supposed to happen! Open a bug report at https://github.com/haskell/happy/issues\n"
 
 -----------------------------------------------------------------------------
 -- Hack to get the typechecker to accept our action functions