diff --git a/collects/redex/private/rewrite-side-conditions.rkt b/collects/redex/private/rewrite-side-conditions.rkt
index f867b43e40..b4847b645f 100644
--- a/collects/redex/private/rewrite-side-conditions.rkt
+++ b/collects/redex/private/rewrite-side-conditions.rkt
@@ -202,7 +202,7 @@
                    (raise-syntax-error
                     what
                     (format "before underscore must be either a non-terminal or a built-in pattern, found ~a in ~s"
-                            suffix-sym (syntax-e term))
+                            prefix-sym (syntax-e term))
                     orig-stx 
                     term)])]
                [(eq? (syntax-e term) '...)