diff --git a/gdk/x11/gdkdisplay-x11.c b/gdk/x11/gdkdisplay-x11.c
index 46421cbf41..659b9fa380 100644
--- a/gdk/x11/gdkdisplay-x11.c
+++ b/gdk/x11/gdkdisplay-x11.c
@@ -1555,7 +1555,6 @@ _gdk_x11_display_open (const gchar *display_name)
   gchar *argv[1];
 
   XClassHint *class_hint;
-  gulong pid;
   gint ignore;
   gint maj, min;
 
@@ -1726,11 +1725,15 @@ _gdk_x11_display_open (const gchar *display_name)
   if (gdk_sm_client_id)
     set_sm_client_id (display, gdk_sm_client_id);
 
-  pid = getpid ();
-  XChangeProperty (display_x11->xdisplay,
-		   display_x11->leader_window,
-		   gdk_x11_get_xatom_by_name_for_display (display, "_NET_WM_PID"),
-		   XA_CARDINAL, 32, PropModeReplace, (guchar *) & pid, 1);
+  if (!gdk_running_in_sandbox ())
+    {
+      /* if sandboxed, we're likely in a pid namespace and would only confuse the wm with this */
+      pid_t pid = getpid ();
+      XChangeProperty (display_x11->xdisplay,
+                       display_x11->leader_window,
+                       gdk_x11_get_xatom_by_name_for_display (display, "_NET_WM_PID"),
+                       XA_CARDINAL, 32, PropModeReplace, (guchar *) & pid, 1);
+    }
 
   /* We don't yet know a valid time. */
   display_x11->user_time = 0;
diff --git a/gdk/x11/gdkwindow-x11.c b/gdk/x11/gdkwindow-x11.c
index e484b58253..00a3a6d268 100644
--- a/gdk/x11/gdkwindow-x11.c
+++ b/gdk/x11/gdkwindow-x11.c
@@ -902,7 +902,6 @@ setup_toplevel_window (GdkWindow *window,
   XID xid = GDK_WINDOW_XID (window);
   GdkX11Screen *x11_screen = GDK_X11_SCREEN (GDK_WINDOW_SCREEN (parent));
   XSizeHints size_hints;
-  long pid;
   Window leader_window;
 
   set_wm_protocols (window);
@@ -933,12 +932,16 @@ setup_toplevel_window (GdkWindow *window,
   /* This will set WM_CLIENT_MACHINE and WM_LOCALE_NAME */
   XSetWMProperties (xdisplay, xid, NULL, NULL, NULL, 0, NULL, NULL, NULL);
   
-  pid = getpid ();
-  XChangeProperty (xdisplay, xid,
-		   gdk_x11_get_xatom_by_name_for_display (x11_screen->display, "_NET_WM_PID"),
-		   XA_CARDINAL, 32,
-		   PropModeReplace,
-		   (guchar *)&pid, 1);
+  if (!gdk_running_in_sandbox ())
+    {
+      /* if sandboxed, we're likely in a pid namespace and would only confuse the wm with this */
+      pid_t pid = getpid ();
+      XChangeProperty (xdisplay, xid,
+                       gdk_x11_get_xatom_by_name_for_display (x11_screen->display, "_NET_WM_PID"),
+                       XA_CARDINAL, 32,
+                       PropModeReplace,
+                       (guchar *)&pid, 1);
+    }
 
   leader_window = GDK_X11_DISPLAY (x11_screen->display)->leader_window;
   if (!leader_window)