diff --git a/sha1_file.c b/sha1_file.c
index b60ae15f70..f5b5bec52f 100644
--- a/sha1_file.c
+++ b/sha1_file.c
@@ -32,7 +32,7 @@
 #define SZ_FMT PRIuMAX
 static inline uintmax_t sz_fmt(size_t s) { return s; }
 
-const unsigned char null_sha1[20];
+const unsigned char null_sha1[GIT_MAX_RAWSZ];
 const struct object_id null_oid;
 const struct object_id empty_tree_oid = {
 	EMPTY_TREE_SHA1_BIN_LITERAL