diff --git a/libtransmission/natpmp.c b/libtransmission/natpmp.c
index 2335bc82e..8f15f89a8 100644
--- a/libtransmission/natpmp.c
+++ b/libtransmission/natpmp.c
@@ -85,10 +85,11 @@ tr_natpmpInit( void )
 void
 tr_natpmpClose( tr_natpmp * nat )
 {
-    assert( !nat->isMapped );
-
-    closenatpmp( &nat->natpmp );
-    tr_free( nat );
+    if( nat )
+    {
+        closenatpmp( &nat->natpmp );
+        tr_free( nat );
+    }
 }
 
 static int