diff --git a/collects/ffi/unsafe/com.rkt b/collects/ffi/unsafe/com.rkt
index 09fb54ffd5..19a0ac62e8 100644
--- a/collects/ffi/unsafe/com.rkt
+++ b/collects/ffi/unsafe/com.rkt
@@ -1864,6 +1864,7 @@
                         method-result))
               (cond
                [(zero? hr)
+                                (log-error (format "result kind: ~s" (VARIANT-vt method-result)))
                 (begin0
                  (if method-result
                      (variant-to-scheme method-result)
diff --git a/collects/racket/private/for.rkt b/collects/racket/private/for.rkt
index 2f466d9f69..ab9e669347 100644
--- a/collects/racket/private/for.rkt
+++ b/collects/racket/private/for.rkt
@@ -1411,7 +1411,7 @@
                                (syntax/loc fc [ids (stop-after
                                                     rhs
                                                     (lambda x
-                                                      (= i len)))])]
+                                                      (unsafe-fx= i len)))])]
                               [_ fc]))
                           (cons wrapped-fc
                                 (loop (cdr fcs) wrap-all?))]))]
diff --git a/collects/tests/racket/optimize.rktl b/collects/tests/racket/optimize.rktl
index ad695ca0d6..2c09c6c342 100644
--- a/collects/tests/racket/optimize.rktl
+++ b/collects/tests/racket/optimize.rktl
@@ -1558,6 +1558,18 @@
                       10
                       (cons (f i) (loop (sub1 n))))))))
 
+(test-comp `(module m racket/base
+              (require racket/unsafe/ops)
+              (define (f x)
+                (let-values ([(a b) (values x (unsafe-fx+ x x))])
+                  (list a b))))
+           `(module m racket/base
+              (require racket/unsafe/ops)
+              (define (f x)
+                (let ([a x]
+                      [b (unsafe-fx+ x x)])
+                  (list a b)))))
+
 ;; check omit & reorder possibilities for unsafe
 ;; operations on mutable values:
 (let ()
diff --git a/src/racket/src/optimize.c b/src/racket/src/optimize.c
index 8238543bd3..5f0a9c8470 100644
--- a/src/racket/src/optimize.c
+++ b/src/racket/src/optimize.c
@@ -372,7 +372,7 @@ int scheme_omittable_expr(Scheme_Object *o, int vals, int fuel, int resolved,
     }
 
     if (SCHEME_PRIMP(app->args[0])) {
-      if ((SCHEME_PRIM_PROC_FLAGS(app->args[0]) & SCHEME_PRIM_IS_OMITABLE)
+      if ((SCHEME_PRIM_PROC_FLAGS(app->args[0]) & (SCHEME_PRIM_IS_OMITABLE | SCHEME_PRIM_IS_UNSAFE_NONMUTATING))
           && (app->num_args >= ((Scheme_Primitive_Proc *)app->args[0])->mina)
           && (app->num_args <= ((Scheme_Primitive_Proc *)app->args[0])->mu.maxa)
           && ((vals < 0) 
@@ -399,7 +399,7 @@ int scheme_omittable_expr(Scheme_Object *o, int vals, int fuel, int resolved,
   if (vtype == scheme_application2_type) {
     Scheme_App2_Rec *app = (Scheme_App2_Rec *)o;
     if (SCHEME_PRIMP(app->rator)) {
-      if ((SCHEME_PRIM_PROC_FLAGS(app->rator) & SCHEME_PRIM_IS_OMITABLE)
+      if ((SCHEME_PRIM_PROC_FLAGS(app->rator) & (SCHEME_PRIM_IS_OMITABLE | SCHEME_PRIM_IS_UNSAFE_NONMUTATING))
           && (1 >= ((Scheme_Primitive_Proc *)app->rator)->mina)
           && (1 <= ((Scheme_Primitive_Proc *)app->rator)->mu.maxa)
           && ((vals < 0) 
@@ -419,7 +419,7 @@ int scheme_omittable_expr(Scheme_Object *o, int vals, int fuel, int resolved,
   if (vtype == scheme_application3_type) {
     Scheme_App3_Rec *app = (Scheme_App3_Rec *)o;
     if (SCHEME_PRIMP(app->rator)) {
-      if ((SCHEME_PRIM_PROC_FLAGS(app->rator) & SCHEME_PRIM_IS_OMITABLE)
+      if ((SCHEME_PRIM_PROC_FLAGS(app->rator) & (SCHEME_PRIM_IS_OMITABLE | SCHEME_PRIM_IS_UNSAFE_NONMUTATING))
           && (2 >= ((Scheme_Primitive_Proc *)app->rator)->mina)
           && (2 <= ((Scheme_Primitive_Proc *)app->rator)->mu.maxa)
           && ((vals < 0) 
@@ -1404,7 +1404,7 @@ static Scheme_Object *check_app_let_rator(Scheme_Object *app, Scheme_Object *rat
 static int is_nonmutating_primitive(Scheme_Object *rator, int n)
 {
   if (SCHEME_PRIMP(rator)
-      && (SCHEME_PRIM_PROC_FLAGS(rator) & SCHEME_PRIM_IS_OMITABLE)
+      && (SCHEME_PRIM_PROC_FLAGS(rator) & (SCHEME_PRIM_IS_OMITABLE | SCHEME_PRIM_IS_UNSAFE_NONMUTATING))
       && (n >= ((Scheme_Primitive_Proc *)rator)->mina)
       && (n <= ((Scheme_Primitive_Proc *)rator)->mu.maxa))
     return 1;