diff --git a/decode.rkt b/decode.rkt
index c2ef829..5639acf 100644
--- a/decode.rkt
+++ b/decode.rkt
@@ -11,7 +11,7 @@
 (define (to-string x)
   (if (string? x)
       x ; fast exit for strings
-      (with-handlers  ([exn:fail? (λ(exn) (error "Can't convert ~a to ~a" x 'string))])
+      (with-handlers  ([exn:fail? (λ(exn) (error (format "Pollen parser: can't convert ~a to ~a" x 'string)))])
         (cond
           [(equal? '() x) ""]
           [(symbol? x) (symbol->string x)]