diff --git a/hash.h b/hash.h
index 756166ce5e..0bf63cedfa 100644
--- a/hash.h
+++ b/hash.h
@@ -305,6 +305,9 @@ struct git_hash_algo {
 
 	/* The all-zeros OID. */
 	const struct object_id *null_oid;
+
+	/* The unsafe variant of this hash function, if one exists. */
+	const struct git_hash_algo *unsafe;
 };
 extern const struct git_hash_algo hash_algos[GIT_HASH_NALGOS];
 
@@ -320,9 +323,17 @@ int hash_algo_by_length(int len);
 /* Identical, except for a pointer to struct git_hash_algo. */
 static inline int hash_algo_by_ptr(const struct git_hash_algo *p)
 {
-	return p - hash_algos;
+	size_t i;
+	for (i = 0; i < GIT_HASH_NALGOS; i++) {
+		const struct git_hash_algo *algop = &hash_algos[i];
+		if (p == algop)
+			return i;
+	}
+	return GIT_HASH_UNKNOWN;
 }
 
+const struct git_hash_algo *unsafe_hash_algo(const struct git_hash_algo *algop);
+
 const struct object_id *null_oid(void);
 
 static inline int hashcmp(const unsigned char *sha1, const unsigned char *sha2, const struct git_hash_algo *algop)
diff --git a/object-file.c b/object-file.c
index 5b792b3dd4..43efa4ca36 100644
--- a/object-file.c
+++ b/object-file.c
@@ -202,6 +202,22 @@ static void git_hash_unknown_final_oid(struct object_id *oid UNUSED,
 	BUG("trying to finalize unknown hash");
 }
 
+static const struct git_hash_algo sha1_unsafe_algo = {
+	.name = "sha1",
+	.format_id = GIT_SHA1_FORMAT_ID,
+	.rawsz = GIT_SHA1_RAWSZ,
+	.hexsz = GIT_SHA1_HEXSZ,
+	.blksz = GIT_SHA1_BLKSZ,
+	.init_fn = git_hash_sha1_init_unsafe,
+	.clone_fn = git_hash_sha1_clone_unsafe,
+	.update_fn = git_hash_sha1_update_unsafe,
+	.final_fn = git_hash_sha1_final_unsafe,
+	.final_oid_fn = git_hash_sha1_final_oid_unsafe,
+	.empty_tree = &empty_tree_oid,
+	.empty_blob = &empty_blob_oid,
+	.null_oid = &null_oid_sha1,
+};
+
 const struct git_hash_algo hash_algos[GIT_HASH_NALGOS] = {
 	{
 		.name = NULL,
@@ -239,6 +255,7 @@ const struct git_hash_algo hash_algos[GIT_HASH_NALGOS] = {
 		.unsafe_update_fn = git_hash_sha1_update_unsafe,
 		.unsafe_final_fn = git_hash_sha1_final_unsafe,
 		.unsafe_final_oid_fn = git_hash_sha1_final_oid_unsafe,
+		.unsafe = &sha1_unsafe_algo,
 		.empty_tree = &empty_tree_oid,
 		.empty_blob = &empty_blob_oid,
 		.null_oid = &null_oid_sha1,
@@ -305,6 +322,15 @@ int hash_algo_by_length(int len)
 	return GIT_HASH_UNKNOWN;
 }
 
+const struct git_hash_algo *unsafe_hash_algo(const struct git_hash_algo *algop)
+{
+	/* If we have a faster "unsafe" implementation, use that. */
+	if (algop->unsafe)
+		return algop->unsafe;
+	/* Otherwise use the default one. */
+	return algop;
+}
+
 /*
  * This is meant to hold a *small* number of objects that you would
  * want repo_read_object_file() to be able to return, but yet you do not want