diff --git a/include/ZeroTierOne.h b/include/ZeroTierOne.h
index 448234693..fd475959d 100644
--- a/include/ZeroTierOne.h
+++ b/include/ZeroTierOne.h
@@ -84,7 +84,7 @@ extern "C" {
 /**
  * Minimum UDP payload size allowed
  */
-#define ZT_MIN_PHYSMTU 1400
+#define ZT_MIN_PHYSMTU 510
 
 /**
  * Maximum physical interface name length. This number is gigantic because of Windows.
diff --git a/node/Topology.hpp b/node/Topology.hpp
index 53c2b6d5b..c0f659ea8 100644
--- a/node/Topology.hpp
+++ b/node/Topology.hpp
@@ -424,6 +424,8 @@ class Topology
 					pc.mtu = ZT_MAX_PHYSMTU;
 				}
 
+				fprintf(stderr,"phy mtu %d\n",pc.mtu);
+
 				cpaths[*(reinterpret_cast<const InetAddress *>(pathNetwork))] = pc;
 			} else {
 				cpaths.erase(*(reinterpret_cast<const InetAddress *>(pathNetwork)));