diff --git a/racket/src/racket/src/string.c b/racket/src/racket/src/string.c
index d6beac752d..818394ac16 100644
--- a/racket/src/racket/src/string.c
+++ b/racket/src/racket/src/string.c
@@ -2214,7 +2214,7 @@ static Scheme_Object *sch_putenv(int argc, Scheme_Object *argv[])
       else {
         scheme_raise_exn(MZEXN_FAIL,
                          "environment-variables-set!: change failed\n"
-                         "  system error: %E");
+                         "  system error: %R");
       }
     }