diff --git a/scheme/cyclone/transforms.sld b/scheme/cyclone/transforms.sld
index 2cb0c371..bb6cbd60 100644
--- a/scheme/cyclone/transforms.sld
+++ b/scheme/cyclone/transforms.sld
@@ -349,6 +349,7 @@
   (and 
     (pair? ast)
     (prim? (car ast))
+    (not (prim:udf? (car ast)))
     ;; Does not make sense to precompute these
     (not (member (car ast)
                 '(Cyc-global-vars