diff --git a/unpack-trees.c b/unpack-trees.c
index 42c7d7d563..f9d12aafba 100644
--- a/unpack-trees.c
+++ b/unpack-trees.c
@@ -128,7 +128,7 @@ static inline int call_unpack_fn(struct cache_entry **src, struct unpack_trees_o
 
 static int unpack_index_entry(struct cache_entry *ce, struct unpack_trees_options *o)
 {
-	struct cache_entry *src[5] = { ce, };
+	struct cache_entry *src[5] = { ce, NULL, };
 
 	o->pos++;
 	if (ce_stage(ce)) {