diff --git a/cache.h b/cache.h
index 85a8e7b101..5d969727f9 100644
--- a/cache.h
+++ b/cache.h
@@ -45,10 +45,14 @@ unsigned long git_deflate_bound(git_zstream *, unsigned long);
 /* The length in bytes and in hex digits of an object name (SHA-1 value). */
 #define GIT_SHA1_RAWSZ 20
 #define GIT_SHA1_HEXSZ (2 * GIT_SHA1_RAWSZ)
+/* The block size of SHA-1. */
+#define GIT_SHA1_BLKSZ 64
 
 /* The length in byte and in hex digits of the largest possible hash value. */
 #define GIT_MAX_RAWSZ GIT_SHA1_RAWSZ
 #define GIT_MAX_HEXSZ GIT_SHA1_HEXSZ
+/* The largest possible block size for any supported hash. */
+#define GIT_MAX_BLKSZ GIT_SHA1_BLKSZ
 
 struct object_id {
 	unsigned char hash[GIT_MAX_RAWSZ];
diff --git a/hash.h b/hash.h
index 80881eea47..1bcf7ab6fd 100644
--- a/hash.h
+++ b/hash.h
@@ -81,6 +81,9 @@ struct git_hash_algo {
 	/* The length of the hash in hex characters. */
 	size_t hexsz;
 
+	/* The block size of the hash. */
+	size_t blksz;
+
 	/* The hash initialization function. */
 	git_hash_init_fn init_fn;
 
diff --git a/sha1-file.c b/sha1-file.c
index 3a75d515eb..9aadaf0c8d 100644
--- a/sha1-file.c
+++ b/sha1-file.c
@@ -90,6 +90,7 @@ const struct git_hash_algo hash_algos[GIT_HASH_NALGOS] = {
 		0x00000000,
 		0,
 		0,
+		0,
 		git_hash_unknown_init,
 		git_hash_unknown_update,
 		git_hash_unknown_final,
@@ -102,6 +103,7 @@ const struct git_hash_algo hash_algos[GIT_HASH_NALGOS] = {
 		0x73686131,
 		GIT_SHA1_RAWSZ,
 		GIT_SHA1_HEXSZ,
+		GIT_SHA1_BLKSZ,
 		git_hash_sha1_init,
 		git_hash_sha1_update,
 		git_hash_sha1_final,