diff --git a/pkgs/racket-test-core/tests/racket/syntax.rktl b/pkgs/racket-test-core/tests/racket/syntax.rktl
index 9417cafaa5..988d57a635 100644
--- a/pkgs/racket-test-core/tests/racket/syntax.rktl
+++ b/pkgs/racket-test-core/tests/racket/syntax.rktl
@@ -2037,4 +2037,19 @@
 
 ;; ;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
 
+(module provide-transformer-set!-and-broken-module-begin racket
+  (provide
+   (for-syntax set!)
+   (rename-out (defined-begin #%module-begin)))
+
+  (define-syntax (defined-begin stx)
+    (syntax-case stx ()
+      [(_ e ...)
+       #`(#%plain-module-begin #,@(map expand (syntax->list #'(e ...))))])))
+
+(err/rt-test (eval '(module m 'provide-transformer-set!-and-broken-module-begin (set! x 1)))
+             exn:fail:syntax?)
+
+;; ;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
+
 (report-errs)
diff --git a/racket/src/racket/src/compenv.c b/racket/src/racket/src/compenv.c
index 312534a646..211b47fac0 100644
--- a/racket/src/racket/src/compenv.c
+++ b/racket/src/racket/src/compenv.c
@@ -692,10 +692,12 @@ void scheme_register_unbound_toplevel(Scheme_Comp_Env *env, Scheme_Object *id)
 {
   Comp_Prefix *cp = env->prefix;
 
-  if (!cp->unbound) cp->unbound = scheme_null;
-
-  id = scheme_make_pair(id, cp->unbound);
-  cp->unbound = id;
+  if (cp) {
+    if (!cp->unbound) cp->unbound = scheme_null;
+    
+    id = scheme_make_pair(id, cp->unbound);
+    cp->unbound = id;
+  }
 }
 
 void scheme_merge_undefineds(Scheme_Comp_Env *exp_env, Scheme_Comp_Env *env)