diff --git a/src/plugins/plugin_misc_nat-port.py b/src/plugins/plugin_misc_nat-port.py
index 9337f932..abdd084a 100644
--- a/src/plugins/plugin_misc_nat-port.py
+++ b/src/plugins/plugin_misc_nat-port.py
@@ -150,12 +150,16 @@ class NatPort(object):
                     #      to avoid testing again the first series the next time
                     self._starting_port_cache = ext_port
 
-            mapping = self._upnp.addportmapping(
-                # the last parameter is remoteHost, we don't use it
-                ext_port, protocol, self._upnp.lanaddr, int_port, desc, '')
+            try:
+                mapping = self._upnp.addportmapping(
+                    # the last parameter is remoteHost, we don't use it
+                    ext_port, protocol, self._upnp.lanaddr, int_port, desc, '')
+            except Exception as e:
+                log.error(_(u"addportmapping error: {msg}").format(msg=e))
+                raise failure.Failure(MappingError())
 
             if not mapping:
-                raise MappingError
+                raise failure.Failure(MappingError())
             else:
                 self._to_unmap.append((ext_port, protocol))
         finally:
@@ -182,9 +186,12 @@ class NatPort(object):
                 ext_port = ext_port,
                 ))
             return ext_port
-        def mappingEb(failure):
-            failure.trap(MappingError)
+        def mappingEb(failure_):
+            failure_.trap(MappingError)
             log.warning(u"Can't map internal {int_port}".format(int_port=int_port))
+        def mappingUnknownEb(failure_):
+            log.error(_(u"error while trying to map ports: {msg}").format(msg=failure_))
         d = threads.deferToThread(self._mapPortBlocking, int_port, ext_port, protocol, desc)
         d.addCallbacks(mappingCb, mappingEb)
+        d.addErrback(mappingUnknownEb)
         return d