diff --git a/reg3.cpp b/reg3.cpp
index e4b92a00..7234d633 100644
--- a/reg3.cpp
+++ b/reg3.cpp
@@ -1714,6 +1714,7 @@ EX }
 #if MAXMDIM == 3
 EX namespace reg3 {
 EX bool in() { return false; }
+EX bool in_rule() { return false; }
 EX }
 #endif