diff --git a/cache.h b/cache.h
index b1bd9e46c..53c23413e 100644
--- a/cache.h
+++ b/cache.h
@@ -217,7 +217,7 @@ extern int commit_locked_index(struct lock_file *);
 extern void set_alternate_index_output(const char *);
 
 extern void rollback_lock_file(struct lock_file *);
-extern int delete_ref(const char *, unsigned char *sha1);
+extern int delete_ref(const char *, const unsigned char *sha1);
 
 /* Environment bits from configuration mechanism */
 extern int use_legacy_headers;
diff --git a/refs.c b/refs.c
index d2b7b7fb5..d7be2841c 100644
--- a/refs.c
+++ b/refs.c
@@ -705,7 +705,7 @@ static int repack_without_ref(const char *refname)
 	return commit_lock_file(&packlock);
 }
 
-int delete_ref(const char *refname, unsigned char *sha1)
+int delete_ref(const char *refname, const unsigned char *sha1)
 {
 	struct ref_lock *lock;
 	int err, i, ret = 0, flag = 0;