diff --git a/revision.c b/revision.c
index 9b9d77d..7f4acad 100644
--- a/revision.c
+++ b/revision.c
@@ -131,10 +131,12 @@
 
 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;