diff --git a/revision.c b/revision.c
index 351fb5b9f..f6caef067 100644
--- a/revision.c
+++ b/revision.c
@@ -135,10 +135,12 @@ static void mark_tree_contents_uninteresting(struct tree *tree)
 
 void mark_tree_uninteresting(struct tree *tree)
 {
-	struct object *obj = &tree->object;
+	struct object *obj;
 
 	if (!tree)
 		return;
+
+	obj = &tree->object;
 	if (obj->flags & UNINTERESTING)
 		return;
 	obj->flags |= UNINTERESTING;