diff --git a/collects/tests/racket/module.rktl b/collects/tests/racket/module.rktl
index 9240457e34..071dd2d9ac 100644
--- a/collects/tests/racket/module.rktl
+++ b/collects/tests/racket/module.rktl
@@ -276,7 +276,6 @@
 ;; ;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
 ;; Test `require' scoping
 
-
 (module fake-prefix-in scheme
   (require scheme/require-syntax)
   (define-require-syntax (pseudo-+ stx)
@@ -702,6 +701,14 @@
             (module-path-index-resolve
              (car (identifier-binding (car (syntax-property #'one 'origin))))))))])
 
+;; ;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
+;; Check that set! of an unbound for-syntax variable is a syntax error
+
+(err/rt-test (expand '(module m racket/base
+                        (require (for-syntax racket/base))
+                        (begin-for-syntax
+                         (lambda () (set! x 6)))))
+             exn:fail:syntax?)
 
 ;; ;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
 
diff --git a/src/racket/src/compenv.c b/src/racket/src/compenv.c
index e103c60bc8..7ce19b82db 100644
--- a/src/racket/src/compenv.c
+++ b/src/racket/src/compenv.c
@@ -1900,17 +1900,24 @@ scheme_lookup_binding(Scheme_Object *find_id, Scheme_Comp_Env *env, int flags,
     genv = env->genv;
     modname = NULL;
 
-    if (genv->module && (genv->disallow_unbound > 0)) {
-      /* Free identifier. Maybe don't continue. */
-      if (flags & (SCHEME_SETTING | SCHEME_REFERENCING)) {
-        scheme_unbound_syntax(((flags & SCHEME_SETTING) 
-                               ? scheme_set_stx_string
-                               : scheme_var_ref_string),
-                              NULL, src_find_id, "unbound identifier in module");
-	return NULL;
+    if (genv->module && genv->disallow_unbound) {
+      if (genv->disallow_unbound > 0) {
+        /* Free identifier. Maybe don't continue. */
+        if (flags & (SCHEME_SETTING | SCHEME_REFERENCING)) {
+          scheme_unbound_syntax(((flags & SCHEME_SETTING) 
+                                 ? scheme_set_stx_string
+                                 : scheme_var_ref_string),
+                                NULL, src_find_id, "unbound identifier in module");
+          return NULL;
+        }
+        if (flags & SCHEME_NULL_FOR_UNBOUND)
+          return NULL;
+      } else {
+        if (flags & (SCHEME_SETTING | SCHEME_REFERENCING)) {
+          scheme_register_unbound_toplevel(env, src_find_id);
+        }
+        /* continue, for now */
       }
-      if (flags & SCHEME_NULL_FOR_UNBOUND)
-	return NULL;
     }
   }