diff --git a/reg3.cpp b/reg3.cpp
index 42389d02..0df0ea7f 100644
--- a/reg3.cpp
+++ b/reg3.cpp
@@ -1608,5 +1608,12 @@ EX void construct_relations() {
 
 EX }
 #endif
+
+#if MAXMDIM == 3
+EX namespace reg3 {
+  bool in() { return false; }
+EX }
+#endif
+
 }