diff --git a/pkgs/racket-test-core/tests/racket/optimize.rktl b/pkgs/racket-test-core/tests/racket/optimize.rktl
index 487a7f7171..6959c90140 100644
--- a/pkgs/racket-test-core/tests/racket/optimize.rktl
+++ b/pkgs/racket-test-core/tests/racket/optimize.rktl
@@ -4039,6 +4039,13 @@
   (check-number-op-unary 'sub1)
   (check-number-op-unary 'abs))
 
+;; `abs` wants and produces reals, not arbitrary numbers:
+(test-comp '(lambda (x) (when (number? x) (abs x)) 5)
+           '(lambda (x) 5)
+           #f)
+(test-comp '(lambda (x) (real? (abs x)))
+           '(lambda (x) (abs x) #t))
+
 (test-comp '(lambda () (-) (void))
            '(lambda () (void))
            #f)
diff --git a/racket/src/racket/src/numarith.c b/racket/src/racket/src/numarith.c
index 6f1aac3921..0da581b917 100644
--- a/racket/src/racket/src/numarith.c
+++ b/racket/src/racket/src/numarith.c
@@ -124,9 +124,9 @@ void scheme_init_numarith(Scheme_Startup_Env *env)
 
   p = scheme_make_folding_prim(scheme_abs, "abs", 1, 1, 1);
   SCHEME_PRIM_PROC_FLAGS(p) |= scheme_intern_prim_opt_flags(SCHEME_PRIM_IS_UNARY_INLINED
-                                                            | SCHEME_PRIM_WANTS_NUMBER
+                                                            | SCHEME_PRIM_WANTS_REAL
                                                             | SCHEME_PRIM_OMITTABLE_ON_GOOD_ARGS
-                                                            | SCHEME_PRIM_PRODUCES_NUMBER
+                                                            | SCHEME_PRIM_PRODUCES_REAL
                                                             | SCHEME_PRIM_CLOSED_ON_REALS);
   scheme_addto_prim_instance("abs", p, env);