diff --git a/src/core/window-private.h b/src/core/window-private.h
index 73174f2eb..713acd3bd 100644
--- a/src/core/window-private.h
+++ b/src/core/window-private.h
@@ -653,9 +653,6 @@ void meta_window_set_transient_for        (MetaWindow *window,
 void meta_window_set_opacity              (MetaWindow *window,
                                            guint8      opacity);
 
-void meta_window_set_custom_frame_extents (MetaWindow *window,
-                                           GtkBorder  *extents);
-
 void meta_window_handle_enter (MetaWindow  *window,
                                guint32      timestamp,
                                guint        root_x,
diff --git a/src/core/window.c b/src/core/window.c
index abf66949a..404d05a16 100644
--- a/src/core/window.c
+++ b/src/core/window.c
@@ -7887,24 +7887,6 @@ meta_window_handle_ungrabbed_event (MetaWindow         *window,
     }
 }
 
-void
-meta_window_set_custom_frame_extents (MetaWindow *window,
-                                      GtkBorder  *extents)
-{
-  if (extents)
-    {
-      window->has_custom_frame_extents = TRUE;
-      window->custom_frame_extents = *extents;
-    }
-  else
-    {
-      window->has_custom_frame_extents = FALSE;
-      memset (&window->custom_frame_extents, 0, sizeof (window->custom_frame_extents));
-    }
-
-  meta_window_queue (window, META_QUEUE_MOVE_RESIZE);
-}
-
 gboolean
 meta_window_can_maximize (MetaWindow *window)
 {
diff --git a/src/x11/window-props.c b/src/x11/window-props.c
index 79cc890c4..1b4fa6e33 100644
--- a/src/x11/window-props.c
+++ b/src/x11/window-props.c
@@ -338,6 +338,24 @@ reload_icon_geometry (MetaWindow    *window,
     }
 }
 
+static void
+meta_window_set_custom_frame_extents (MetaWindow *window,
+                                      GtkBorder  *extents)
+{
+  if (extents)
+    {
+      window->has_custom_frame_extents = TRUE;
+      window->custom_frame_extents = *extents;
+    }
+  else
+    {
+      window->has_custom_frame_extents = FALSE;
+      memset (&window->custom_frame_extents, 0, sizeof (window->custom_frame_extents));
+    }
+
+  meta_window_queue (window, META_QUEUE_MOVE_RESIZE);
+}
+
 static void
 reload_gtk_frame_extents (MetaWindow    *window,
                           MetaPropValue *value,