diff --git a/drivers/gpu/drm/rockchip/rockchip_drm_gem.c b/drivers/gpu/drm/rockchip/rockchip_drm_gem.c
index 9426f7976d22..10a4970ad2d8 100644
--- a/drivers/gpu/drm/rockchip/rockchip_drm_gem.c
+++ b/drivers/gpu/drm/rockchip/rockchip_drm_gem.c
@@ -39,7 +39,7 @@ static int rockchip_gem_iommu_map(struct rockchip_gem_object *rk_obj)
 
 	ret = iommu_map_sgtable(private->domain, rk_obj->dma_addr, rk_obj->sgt,
 				prot);
-	if (ret < rk_obj->base.size) {
+	if (ret < (ssize_t)rk_obj->base.size) {
 		DRM_ERROR("failed to map buffer: size=%zd request_size=%zd\n",
 			  ret, rk_obj->base.size);
 		ret = -ENOMEM;