diff --git a/libweston/compositor.c b/libweston/compositor.c
index 2d3b0aa31..db8b14a53 100644
--- a/libweston/compositor.c
+++ b/libweston/compositor.c
@@ -4305,7 +4305,8 @@ weston_surface_is_pending_viewport_source_valid(
 	if (vp->buffer.src_width == wl_fixed_from_int(-1))
 		return true;
 
-	if (pend->status & WESTON_SURFACE_DIRTY_BUFFER) {
+	if ((pend->status & WESTON_SURFACE_DIRTY_BUFFER) ||
+		(pend->status & WESTON_SURFACE_DIRTY_SIZE)) {
 		if (pend->buffer) {
 			convert_size_by_transform_scale(&width_from_buffer,
 							&height_from_buffer,