diff --git a/src/core/window-private.h b/src/core/window-private.h
index d6de1256c..ed5d8059b 100644
--- a/src/core/window-private.h
+++ b/src/core/window-private.h
@@ -548,6 +548,8 @@ struct _MetaWindow
   } placement;
 
   guint unmanage_idle_id;
+
+  pid_t client_pid;
 };
 
 struct _MetaWindowClass
diff --git a/src/core/window.c b/src/core/window.c
index b2a7be5dd..d7faf00fc 100644
--- a/src/core/window.c
+++ b/src/core/window.c
@@ -1149,6 +1149,8 @@ _meta_window_shared_new (MetaDisplay         *display,
   window->is_remote = FALSE;
   window->startup_id = NULL;
 
+  window->client_pid = 0;
+
   window->xtransient_for = None;
   window->xclient_leader = None;
 
@@ -7595,7 +7597,10 @@ meta_window_get_pid (MetaWindow *window)
 {
   g_return_val_if_fail (META_IS_WINDOW (window), 0);
 
-  return META_WINDOW_GET_CLASS (window)->get_client_pid (window);
+  if (window->client_pid == 0)
+    window->client_pid = META_WINDOW_GET_CLASS (window)->get_client_pid (window);
+
+  return window->client_pid;
 }
 
 /**