diff --git a/gdk/gdkdevicetool.c b/gdk/gdkdevicetool.c
index 54076b6481..3f0781128a 100644
--- a/gdk/gdkdevicetool.c
+++ b/gdk/gdkdevicetool.c
@@ -145,7 +145,7 @@ gdk_device_tool_new (guint64           serial,
  *
  * Since: 3.22
  **/
-guint
+guint64
 gdk_device_tool_get_serial (GdkDeviceTool *tool)
 {
   g_return_val_if_fail (tool != NULL, 0);
diff --git a/gdk/gdkdevicetool.h b/gdk/gdkdevicetool.h
index 9a00d8a866..5486e7e4eb 100644
--- a/gdk/gdkdevicetool.h
+++ b/gdk/gdkdevicetool.h
@@ -65,7 +65,7 @@ GDK_AVAILABLE_IN_3_22
 GType gdk_device_tool_get_type (void) G_GNUC_CONST;
 
 GDK_AVAILABLE_IN_3_22
-guint gdk_device_tool_get_serial (GdkDeviceTool *tool);
+guint64 gdk_device_tool_get_serial (GdkDeviceTool *tool);
 
 GDK_AVAILABLE_IN_3_22
 GdkDeviceToolType gdk_device_tool_get_tool_type (GdkDeviceTool *tool);