diff --git a/build/valgrind/x86_64-pc-linux-gnu.sup b/build/valgrind/x86_64-pc-linux-gnu.sup
index a0b90b469ea4..0887290e5d7d 100644
--- a/build/valgrind/x86_64-pc-linux-gnu.sup
+++ b/build/valgrind/x86_64-pc-linux-gnu.sup
@@ -257,6 +257,26 @@
     fun:do_main
     fun:main
 }
+{
+    gtk3/X11 leaks x11 child GdkWindow internals (Bug 1864382)
+    Memcheck:Leak
+    match-leak-kinds: definite
+    ...
+    fun:g_object_new
+    fun:_gdk_x11_display_create_window_impl
+    fun:gdk_window_ensure_native
+    fun:gdk_x11_window_get_xid
+    fun:GetX11Window
+    ...
+    fun:gtk_widget_map
+    fun:gtk_window_map
+    ...
+    fun:gtk_widget_map
+    fun:gtk_window_show
+    ...
+    fun:gtk_widget_show
+    ...
+}
 
 ###################################
 #  Leaks in short lived processes #