diff --git a/collects/typed-scheme/private/extra-procs.rkt b/collects/typed-scheme/private/extra-procs.rkt
index 6cd86438..b4a74b03 100644
--- a/collects/typed-scheme/private/extra-procs.rkt
+++ b/collects/typed-scheme/private/extra-procs.rkt
@@ -1,8 +1,10 @@
 #lang scheme/base
 (provide assert)
 
-(define (assert v [pred values])
-  (unless (pred v)
-    (error "Assertion failed"))
-  v)
-
+(define-syntax assert
+  (syntax-rules ()
+    ((assert v)
+     (or v (error "Assertion failed")))
+    ((assert v pred)
+     (let ((val v))
+       (if (pred val) val (error "Assertion failed"))))))