diff --git a/pkgs/base/info.rkt b/pkgs/base/info.rkt
index 083bc07ab6..ab15f0b1f7 100644
--- a/pkgs/base/info.rkt
+++ b/pkgs/base/info.rkt
@@ -12,7 +12,7 @@
 
 (define collection 'multi)
 
-(define version "6.11.0.2")
+(define version "6.11.0.3")
 
 (define deps `("racket-lib"
                ["racket" #:version ,version]))
diff --git a/pkgs/racket-test-core/tests/racket/optimize.rktl b/pkgs/racket-test-core/tests/racket/optimize.rktl
index 588055e7f9..3e43555e87 100644
--- a/pkgs/racket-test-core/tests/racket/optimize.rktl
+++ b/pkgs/racket-test-core/tests/racket/optimize.rktl
@@ -6043,6 +6043,15 @@
             (test 'fail "compilation took too long" (/ b a 1.0))
             (loop (sub1 tries)))))))
 
+;; ;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
+;; Make sure the optimizer doesn't assume that `bytes-utf-8-{length,index}`
+;; returns a fixnum:
+
+(test #f 'not-utf-8 (bytes-utf-8-length (bytes 255)))
+(test #t 'not-not-utf-8 (not (bytes-utf-8-length (bytes 255))))
+(test #f 'not-utf-8 (bytes-utf-8-index (bytes 255) 1))
+(test #t 'not-not-utf-8 (not (bytes-utf-8-index (bytes 255) 1)))
+
 ;; ;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
 ;; Try a program that triggers lots of inlining, which at one point
 ;; exposed a bug related to the closing of `lambda` forms within
diff --git a/racket/src/racket/src/schvers.h b/racket/src/racket/src/schvers.h
index 6341193bfa..7d4f05b388 100644
--- a/racket/src/racket/src/schvers.h
+++ b/racket/src/racket/src/schvers.h
@@ -13,12 +13,12 @@
    consistently.)
 */
 
-#define MZSCHEME_VERSION "6.11.0.2"
+#define MZSCHEME_VERSION "6.11.0.3"
 
 #define MZSCHEME_VERSION_X 6
 #define MZSCHEME_VERSION_Y 11
 #define MZSCHEME_VERSION_Z 0
-#define MZSCHEME_VERSION_W 2
+#define MZSCHEME_VERSION_W 3
 
 #define MZSCHEME_VERSION_MAJOR ((MZSCHEME_VERSION_X * 100) + MZSCHEME_VERSION_Y)
 #define MZSCHEME_VERSION_MINOR ((MZSCHEME_VERSION_Z * 1000) + MZSCHEME_VERSION_W)
diff --git a/racket/src/racket/src/string.c b/racket/src/racket/src/string.c
index 818394ac16..799b6be1d2 100644
--- a/racket/src/racket/src/string.c
+++ b/racket/src/racket/src/string.c
@@ -677,11 +677,13 @@ scheme_init_string (Scheme_Env *env)
 			     env);
 
   p = scheme_make_immed_prim(byte_string_utf8_index, "bytes-utf-8-index", 2, 4);
-  SCHEME_PRIM_PROC_FLAGS(p) |= scheme_intern_prim_opt_flags(SCHEME_PRIM_PRODUCES_FIXNUM);
+  /* Incorrect, since the result can be #f:
+     SCHEME_PRIM_PROC_FLAGS(p) |= scheme_intern_prim_opt_flags(SCHEME_PRIM_PRODUCES_FIXNUM); */
   scheme_add_global_constant("bytes-utf-8-index", p, env);
 
   p = scheme_make_immed_prim(byte_string_utf8_length, "bytes-utf-8-length", 1, 4);
-  SCHEME_PRIM_PROC_FLAGS(p) |= scheme_intern_prim_opt_flags(SCHEME_PRIM_PRODUCES_FIXNUM);
+  /* Incorrect, since the result can be #f:
+     SCHEME_PRIM_PROC_FLAGS(p) |= scheme_intern_prim_opt_flags(SCHEME_PRIM_PRODUCES_FIXNUM); */
   scheme_add_global_constant("bytes-utf-8-length", p, env);
 
   scheme_add_global_constant("bytes-utf-8-ref",