diff --git a/gdk/wayland/gdkdevice-wayland.c b/gdk/wayland/gdkdevice-wayland.c
index 20d28bf4e2..2a051de4da 100644
--- a/gdk/wayland/gdkdevice-wayland.c
+++ b/gdk/wayland/gdkdevice-wayland.c
@@ -214,9 +214,12 @@ gdk_device_core_window_at_position (GdkDevice       *device,
   GdkWaylandDevice *wd;
 
   wd = GDK_DEVICE_CORE(device)->device;
-  *win_x = wd->surface_x;
-  *win_y = wd->surface_y;
-  *mask = wd->modifiers;
+  if (win_x)
+    *win_x = wd->surface_x;
+  if (win_y)
+    *win_y = wd->surface_y;
+  if (mask)
+    *mask = wd->modifiers;
 
   return wd->pointer_focus;
 }