diff --git a/drivers/gpu/drm/drm_dp_mst_topology.c b/drivers/gpu/drm/drm_dp_mst_topology.c
index 7780567aa6692fa56450aed78ff101b294fe7da6..d708472d93c4210b71eff4bf1c862f700d8d5876 100644
--- a/drivers/gpu/drm/drm_dp_mst_topology.c
+++ b/drivers/gpu/drm/drm_dp_mst_topology.c
@@ -1274,6 +1274,9 @@ static struct drm_dp_mst_branch *drm_dp_get_mst_branch_device(struct drm_dp_mst_
 	mutex_lock(&mgr->lock);
 	mstb = mgr->mst_primary;
 
+	if (!mstb)
+		goto out;
+
 	for (i = 0; i < lct - 1; i++) {
 		int shift = (i % 2) ? 0 : 4;
 		int port_num = (rad[i / 2] >> shift) & 0xf;