diff --git a/pkgs/racket-test-core/tests/racket/optimize.rktl b/pkgs/racket-test-core/tests/racket/optimize.rktl
index 09dcc34a5f..6e434d5cd3 100644
--- a/pkgs/racket-test-core/tests/racket/optimize.rktl
+++ b/pkgs/racket-test-core/tests/racket/optimize.rktl
@@ -152,6 +152,10 @@
            '(if (pair? null) 89 88))
 (test-comp 89
            '(if (list? null) 89 88))
+(test-comp 0
+           '(length '()))
+(test-comp 3
+           '(length '(1 2 3)))
 
 (test-comp '(lambda (x) (if x 2 1))
            '(lambda (x) (if (not x) 1 2)))
diff --git a/racket/src/racket/src/optimize.c b/racket/src/racket/src/optimize.c
index e37fb351c7..7ab318c16c 100644
--- a/racket/src/racket/src/optimize.c
+++ b/racket/src/racket/src/optimize.c
@@ -4520,6 +4520,12 @@ static Scheme_Object *finish_optimize_application2(Scheme_App2_Rec *app, Optimiz
       }
     }
 
+    if (IS_NAMED_PRIM(rator, "length")
+        && SCHEME_LISTP(rand)) {
+      alt = scheme_make_integer(scheme_list_length(rand));
+      return replace_tail_inside(alt, inside, app->rand);
+    }
+
     alt = try_reduce_predicate(rator, rand, info);
     if (alt)
       return replace_tail_inside(alt, inside, app->rand);