diff --git a/src/Data/Syntax.hs b/src/Data/Syntax.hs
index 0e0735b33..40e943b55 100644
--- a/src/Data/Syntax.hs
+++ b/src/Data/Syntax.hs
@@ -110,7 +110,7 @@ instance Show1 Identifier where liftShowsPrec = genericLiftShowsPrec
 instance Evaluatable Identifier where
   eval (Identifier name) = do
     env <- askLocalEnv
-    maybe (fail ("free variable: " <> show name)) deref (envLookup name env)
+    maybe (fail ("free variable: " <> show (friendlyName name))) deref (envLookup name env)
 
 instance FreeVariables1 Identifier where
   liftFreeVariables _ (Identifier x) = Set.singleton x