diff --git a/color.ml b/color.ml
index bab7edc909213aa9f0ce87a6ab2f404c1619a58c..e17e757de95a1ee36a2f08d37352bbc65c16f887 100644
--- a/color.ml
+++ b/color.ml
@@ -38,7 +38,7 @@ let rec short = function
 
   (* rgb(r,g,b) -> #rrggbb *)
   | Function ("rgb", Nary (",", [r; g; b]))
-    when is_num r & is_num g & is_num b ->
+    when is_num r && is_num g && is_num b ->
     let i c =
       match clip c with
       | Number (n, None) -> int_of_float n