diff --git a/spec/traits.dd b/spec/traits.dd
index 39c2590383..ace86c8107 100644
--- a/spec/traits.dd
+++ b/spec/traits.dd
@@ -1872,6 +1872,9 @@ void main()
         $(P The order in which the strings appear in the result
         is not defined.)
 
+        $(P `WARNING:` If you're trying to iterate only data members,
+        use the builtin property .tupleof instead.)
+
 $(H3 $(GNAME derivedMembers))
 
         $(P Takes a single argument, which must evaluate to either