diff --git a/group.cpp b/group.cpp
index a1d33cc8dc..9b8acb6f99 100644
--- a/group.cpp
+++ b/group.cpp
@@ -211,7 +211,8 @@ bool Client::belongToSameApplication( const Client* c1, const Client* c2, bool a
         ; // different apps
     else if( !sameAppWindowRoleMatch( c1, c2, active_hack ))
         ; // "different" apps
-    else
+    else if( c1->pid() == 0 || c2->pid() == 0 )
+        ; // old apps that don't have _NET_WM_PID, consider them different
         same_app = true; // looks like it's the same app
     return same_app;
     }