diff --git a/node/Constants.hpp b/node/Constants.hpp
index 82d254594..c9202fc04 100644
--- a/node/Constants.hpp
+++ b/node/Constants.hpp
@@ -443,4 +443,9 @@
  */
 #define ZT_TEST_NETWORK_ID 0xffffffffffffffffULL
 
+/**
+ * Enable support for legacy <1.0.0 multicast peers (P5)
+ */
+#define ZT_SUPPORT_LEGACY_MULTICAST 1
+
 #endif