diff --git a/collects/tests/mzscheme/optimize.ss b/collects/tests/mzscheme/optimize.ss
index 983f35ef78..8873ea658a 100644
--- a/collects/tests/mzscheme/optimize.ss
+++ b/collects/tests/mzscheme/optimize.ss
@@ -229,6 +229,8 @@
 	     (let ([v (make-X 3 def-val)])
 	       (check-error-message set-name (eval `(lambda (x) (,set-name ,v -1 ,set-val))))
 	       (check-error-message set-name (eval `(lambda (x) (,set-name ,v 3 ,set-val))))
+               (unless (integer? set-val)
+                 (check-error-message set-name (eval `(lambda (x) (,set-name ,v 0 12)))))
 	       (for-each (lambda (i)
 			   (tri-exact (void) set-name (lambda () v) i set-val
 				      (lambda ()
diff --git a/src/mzscheme/src/jit.c b/src/mzscheme/src/jit.c
index 074fa962c9..979175abf5 100644
--- a/src/mzscheme/src/jit.c
+++ b/src/mzscheme/src/jit.c
@@ -4405,6 +4405,7 @@ static int do_generate_common(mz_jit_state *jitter, void *_data)
 	    jit_stxr_p(JIT_V1, JIT_R0, JIT_R2);
 	    break;
 	  case 1:
+            (void)jit_bmsi_l(reffail, JIT_R2, 0x1);
 	    jit_ldxi_s(JIT_R2, JIT_R2, &((Scheme_Object *)0x0)->type);
 	    (void)jit_bnei_i(reffail, JIT_R2, scheme_char_type);
 	    jit_ldr_p(JIT_R2, JIT_RUNSTACK);