diff --git a/test/libdrm_mock.c b/test/libdrm_mock.c
index a180395..e2ffbf8 100644
--- a/test/libdrm_mock.c
+++ b/test/libdrm_mock.c
@@ -206,6 +206,12 @@ liftoff_mock_plane_add_compatible_layer(struct liftoff_mock_plane *plane,
 	abort(); // unreachable
 }
 
+uint32_t
+liftoff_mock_plane_get_id(struct liftoff_mock_plane *plane)
+{
+	return plane->id;
+}
+
 uint32_t
 liftoff_mock_drm_create_fb(struct liftoff_layer *layer)
 {
diff --git a/test/libdrm_mock.h b/test/libdrm_mock.h
index e2e60ba..54a2a85 100644
--- a/test/libdrm_mock.h
+++ b/test/libdrm_mock.h
@@ -37,6 +37,8 @@ liftoff_mock_plane_add_compatible_layer(struct liftoff_mock_plane *plane,
 					struct liftoff_layer *layer);
 struct liftoff_layer *
 liftoff_mock_plane_get_layer(struct liftoff_mock_plane *plane);
+uint32_t
+liftoff_mock_plane_get_id(struct liftoff_mock_plane *plane);
 
 uint32_t
 liftoff_mock_plane_add_property(struct liftoff_mock_plane *plane,