diff --git a/pkgs/racket-test-core/tests/racket/optimize.rktl b/pkgs/racket-test-core/tests/racket/optimize.rktl
index 2cb9b635cf..ddafff0d82 100644
--- a/pkgs/racket-test-core/tests/racket/optimize.rktl
+++ b/pkgs/racket-test-core/tests/racket/optimize.rktl
@@ -5705,6 +5705,22 @@
         'bar)))
   bar)
 
+;; ;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
+;; Check that `string-append` on a known-string argument
+;; is not treated consistently by the optimzier and
+;; validator
+
+(let ([c (compile
+          '(module m racket/base
+            (define ill
+              (let ((base (string-append "a")))
+                (λ (x) (string-append base x))))
+            (ill "b")))])
+  (define o (open-output-bytes))
+  (write c o)
+  (parameterize ([read-accept-compiled #t])
+    (void (read (open-input-bytes (get-output-bytes o))))))
+
 ;; ;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
 
 (report-errs)
diff --git a/racket/src/racket/src/optimize.c b/racket/src/racket/src/optimize.c
index 868bca0da7..8f4fb46135 100644
--- a/racket/src/racket/src/optimize.c
+++ b/racket/src/racket/src/optimize.c
@@ -8737,7 +8737,7 @@ module_optimize(Scheme_Object *data, Optimize_Info *info, int context)
         if (n == 1) {
           if (scheme_ir_propagate_ok(e, info))
             cnst = 1;
-          else if (scheme_is_statically_proc(e, info, 0)) {
+          else if (scheme_is_statically_proc(e, info, OMITTABLE_IGNORE_APPN_OMIT)) {
             cnst = 1;
             sproc = 1;
           }