diff --git a/router/java/src/net/i2p/router/transport/udp/OutboundMessageFragments.java b/router/java/src/net/i2p/router/transport/udp/OutboundMessageFragments.java
index 8c0f30f28..4f2c9a2d8 100644
--- a/router/java/src/net/i2p/router/transport/udp/OutboundMessageFragments.java
+++ b/router/java/src/net/i2p/router/transport/udp/OutboundMessageFragments.java
@@ -53,7 +53,7 @@ class OutboundMessageFragments {
     /**
      *  Avoid sync in add() if possible (not 100% reliable)
      */
-    private boolean _isWaiting;
+    private volatile boolean _isWaiting;
 
     private volatile boolean _alive;
     private final PacketBuilder _builder;