diff --git a/utils.rkt b/utils.rkt
index 8faf33d..a9ca75d 100644
--- a/utils.rkt
+++ b/utils.rkt
@@ -561,9 +561,15 @@
               (-> Integer Integer (Sequenceof Nonnegative-Fixnum))))
 (define in-random
   (case-lambda
-    [() (stream-cons (random) (in-random))]
-    [(k) (stream-cons (random k) (in-random k))]
-    [(min max) (stream-cons (random min max) (in-random min max))]))
+    [() (stream-cons
+         (assert-type (random) Flonum)
+         (in-random))]
+    [(k) (stream-cons
+          (assert-type (random k) Nonnegative-Fixnum)
+          (in-random k))]
+    [(min max) (stream-cons
+                (assert-type (random min max) Nonnegative-Fixnum)
+                (in-random min max))]))
 
 (module+ test
   (test-case "in-random"