diff --git a/history.txt b/history.txt
index 229e72fdcc..7ec5b7bcc9 100644
--- a/history.txt
+++ b/history.txt
@@ -1,3 +1,7 @@
+2015-10-31 zzz
+ * Convert remaining Threads to I2PThread or I2PAppThread
+ * UPnP: Fix deadlock in callbacks (ticket #1699)
+
 2015-10-30 zzz
  * Router: Fix cascading I2CP error (ticket #1692)
 
diff --git a/router/java/src/net/i2p/router/RouterVersion.java b/router/java/src/net/i2p/router/RouterVersion.java
index f5c9264549..43dca92409 100644
--- a/router/java/src/net/i2p/router/RouterVersion.java
+++ b/router/java/src/net/i2p/router/RouterVersion.java
@@ -18,7 +18,7 @@ public class RouterVersion {
     /** deprecated */
     public final static String ID = "Monotone";
     public final static String VERSION = CoreVersion.VERSION;
-    public final static long BUILD = 20;
+    public final static long BUILD = 21;
 
     /** for example "-test" */
     public final static String EXTRA = "";
diff --git a/router/java/src/net/i2p/router/transport/UPnPManager.java b/router/java/src/net/i2p/router/transport/UPnPManager.java
index 370ba813e8..9d7a6918a0 100644
--- a/router/java/src/net/i2p/router/transport/UPnPManager.java
+++ b/router/java/src/net/i2p/router/transport/UPnPManager.java
@@ -233,7 +233,17 @@ class UPnPManager {
         public void portForwardStatus(Map<ForwardPort,ForwardPortStatus> statuses) {
             if (_log.shouldLog(Log.DEBUG))
                  _log.debug("UPnP Callback:");
+            // Let's not have two of these running at once.
+            // Deadlock reported in ticket #1699
+            // and the locking isn't foolproof in UDPTransport.
+            // UPnP runs the callbacks in a thread, so we can block.
+            // There is only one UPnPCallback, so lock on this
+            synchronized(this) {
+                locked_PFS(statuses);
+            }
+        }
 
+        private void locked_PFS(Map<ForwardPort,ForwardPortStatus> statuses) {
             byte[] ipaddr = null;
             DetectedIP[] ips = _upnp.getAddress();
             if (ips != null) {
@@ -244,6 +254,7 @@ class UPnPManager {
                             _log.debug("External address: " + ip.publicAddress + " type: " + ip.natType);
                         if (!ip.publicAddress.equals(_detectedAddress)) {
                             _detectedAddress = ip.publicAddress;
+                            // deadlock path 1
                             _manager.externalAddressReceived(SOURCE_UPNP, _detectedAddress.getAddress(), 0);
                         }
                         ipaddr = ip.publicAddress.getAddress();
@@ -269,6 +280,7 @@ class UPnPManager {
                 else
                     continue;
                 boolean success = fps.status >= ForwardPortStatus.MAYBE_SUCCESS;
+                // deadlock path 2
                 _manager.forwardPortStatus(style, ipaddr, fp.portNumber, fps.externalPort, success, fps.reasonString);
             }
         }
diff --git a/router/java/src/net/i2p/router/transport/udp/UDPTransport.java b/router/java/src/net/i2p/router/transport/udp/UDPTransport.java
index 223f655f5a..edcfef26bb 100644
--- a/router/java/src/net/i2p/router/transport/udp/UDPTransport.java
+++ b/router/java/src/net/i2p/router/transport/udp/UDPTransport.java
@@ -993,6 +993,7 @@ public class UDPTransport extends TransportImpl implements TimedWeightedPriority
                 // save PROP_EXTERNAL_PORT
                 _context.router().saveConfig(changes, null);
             }
+            // deadlock thru here ticket #1699
             _context.router().rebuildRouterInfo();
         }
         _testEvent.forceRunImmediately();
@@ -2115,6 +2116,7 @@ public class UDPTransport extends TransportImpl implements TimedWeightedPriority
      *  @since 0.9.18
      */
     private RouterAddress getCurrentExternalAddress(boolean isIPv6) {
+        // deadlock thru here ticket #1699
         synchronized (_rebuildLock) {
             return isIPv6 ? _currentOurV6Address : _currentOurV4Address;
         }