diff --git a/cache.h b/cache.h
index 614040e700..071eecee7a 100644
--- a/cache.h
+++ b/cache.h
@@ -813,6 +813,7 @@ extern const char *find_unique_abbrev(const unsigned char *sha1, int len);
 extern int find_unique_abbrev_r(char *hex, const unsigned char *sha1, int len);
 
 extern const unsigned char null_sha1[GIT_SHA1_RAWSZ];
+extern const struct object_id null_oid;
 
 static inline int hashcmp(const unsigned char *sha1, const unsigned char *sha2)
 {
diff --git a/sha1_file.c b/sha1_file.c
index 27ce7b705e..a54deb0558 100644
--- a/sha1_file.c
+++ b/sha1_file.c
@@ -36,6 +36,7 @@
 static inline uintmax_t sz_fmt(size_t s) { return s; }
 
 const unsigned char null_sha1[20];
+const struct object_id null_oid;
 
 /*
  * This is meant to hold a *small* number of objects that you would