diff --git a/reftable/basics.c b/reftable/basics.c
index 10b234ea55..3b5ea27bbd 100644
--- a/reftable/basics.c
+++ b/reftable/basics.c
@@ -272,7 +272,7 @@ size_t common_prefix_size(struct reftable_buf *a, struct reftable_buf *b)
 	return p;
 }
 
-int hash_size(enum reftable_hash id)
+uint32_t hash_size(enum reftable_hash id)
 {
 	if (!id)
 		return REFTABLE_HASH_SIZE_SHA1;
diff --git a/reftable/basics.h b/reftable/basics.h
index 9ff81a68f8..a2a010a0e1 100644
--- a/reftable/basics.h
+++ b/reftable/basics.h
@@ -171,7 +171,7 @@ static inline void *reftable_alloc_grow(void *p, size_t nelem, size_t elsize,
 /* Find the longest shared prefix size of `a` and `b` */
 size_t common_prefix_size(struct reftable_buf *a, struct reftable_buf *b);
 
-int hash_size(enum reftable_hash id);
+uint32_t hash_size(enum reftable_hash id);
 
 /*
  * Format IDs that identify the hash function used by a reftable. Note that
diff --git a/reftable/block.c b/reftable/block.c
index 9858bbc7c5..2380aabb2f 100644
--- a/reftable/block.c
+++ b/reftable/block.c
@@ -72,7 +72,7 @@ static int block_writer_register_restart(struct block_writer *w, int n,
 }
 
 int block_writer_init(struct block_writer *bw, uint8_t typ, uint8_t *block,
-		      uint32_t block_size, uint32_t header_off, int hash_size)
+		      uint32_t block_size, uint32_t header_off, uint32_t hash_size)
 {
 	bw->block = block;
 	bw->hash_size = hash_size;
@@ -214,7 +214,7 @@ int block_writer_finish(struct block_writer *w)
 
 int block_reader_init(struct block_reader *br, struct reftable_block *block,
 		      uint32_t header_off, uint32_t table_block_size,
-		      int hash_size)
+		      uint32_t hash_size)
 {
 	uint32_t full_block_size = table_block_size;
 	uint8_t typ = block->data[header_off];
diff --git a/reftable/block.h b/reftable/block.h
index 0431e8591f..5f67ed74c5 100644
--- a/reftable/block.h
+++ b/reftable/block.h
@@ -30,7 +30,7 @@ struct block_writer {
 
 	/* How often to restart keys. */
 	uint16_t restart_interval;
-	int hash_size;
+	uint32_t hash_size;
 
 	/* Offset of next uint8_t to write. */
 	uint32_t next;
@@ -48,7 +48,7 @@ struct block_writer {
  * initializes the blockwriter to write `typ` entries, using `block` as temporary
  * storage. `block` is not owned by the block_writer. */
 int block_writer_init(struct block_writer *bw, uint8_t typ, uint8_t *block,
-		      uint32_t block_size, uint32_t header_off, int hash_size);
+		      uint32_t block_size, uint32_t header_off, uint32_t hash_size);
 
 /* returns the block type (eg. 'r' for ref records. */
 uint8_t block_writer_type(struct block_writer *bw);
@@ -72,7 +72,7 @@ struct block_reader {
 
 	/* the memory block */
 	struct reftable_block block;
-	int hash_size;
+	uint32_t hash_size;
 
 	/* Uncompressed data for log entries. */
 	z_stream *zstream;
@@ -92,7 +92,7 @@ struct block_reader {
 /* initializes a block reader. */
 int block_reader_init(struct block_reader *br, struct reftable_block *bl,
 		      uint32_t header_off, uint32_t table_block_size,
-		      int hash_size);
+		      uint32_t hash_size);
 
 void block_reader_release(struct block_reader *br);
 
@@ -108,7 +108,7 @@ struct block_iter {
 	uint32_t next_off;
 	const unsigned char *block;
 	size_t block_len;
-	int hash_size;
+	uint32_t hash_size;
 
 	/* key for last entry we read. */
 	struct reftable_buf last_key;
diff --git a/reftable/reader.c b/reftable/reader.c
index ea82955c9b..9df8a5ecb1 100644
--- a/reftable/reader.c
+++ b/reftable/reader.c
@@ -750,7 +750,7 @@ static int reftable_reader_refs_for_unindexed(struct reftable_reader *r,
 	struct table_iter *ti;
 	struct filtering_ref_iterator *filter = NULL;
 	struct filtering_ref_iterator empty = FILTERING_REF_ITERATOR_INIT;
-	int oid_len = hash_size(r->hash_id);
+	uint32_t oid_len = hash_size(r->hash_id);
 	int err;
 
 	REFTABLE_ALLOC_ARRAY(ti, 1);
diff --git a/reftable/record.c b/reftable/record.c
index 4a3e019528..f7766a32ef 100644
--- a/reftable/record.c
+++ b/reftable/record.c
@@ -229,7 +229,7 @@ static int reftable_ref_record_key(const void *r, struct reftable_buf *dest)
 }
 
 static int reftable_ref_record_copy_from(void *rec, const void *src_rec,
-					 int hash_size)
+					 uint32_t hash_size)
 {
 	struct reftable_ref_record *ref = rec;
 	const struct reftable_ref_record *src = src_rec;
@@ -237,8 +237,6 @@ static int reftable_ref_record_copy_from(void *rec, const void *src_rec,
 	size_t refname_cap = 0;
 	int err;
 
-	assert(hash_size > 0);
-
 	SWAP(refname, ref->refname);
 	SWAP(refname_cap, ref->refname_cap);
 	reftable_ref_record_release(ref);
@@ -319,13 +317,12 @@ static uint8_t reftable_ref_record_val_type(const void *rec)
 }
 
 static int reftable_ref_record_encode(const void *rec, struct string_view s,
-				      int hash_size)
+				      uint32_t hash_size)
 {
 	const struct reftable_ref_record *r =
 		(const struct reftable_ref_record *)rec;
 	struct string_view start = s;
 	int n = put_var_int(&s, r->update_index);
-	assert(hash_size > 0);
 	if (n < 0)
 		return -1;
 	string_view_consume(&s, n);
@@ -365,7 +362,7 @@ static int reftable_ref_record_encode(const void *rec, struct string_view s,
 
 static int reftable_ref_record_decode(void *rec, struct reftable_buf key,
 				      uint8_t val_type, struct string_view in,
-				      int hash_size, struct reftable_buf *scratch)
+				      uint32_t hash_size, struct reftable_buf *scratch)
 {
 	struct reftable_ref_record *r = rec;
 	struct string_view start = in;
@@ -374,8 +371,6 @@ static int reftable_ref_record_decode(void *rec, struct reftable_buf key,
 	size_t refname_cap = 0;
 	int n, err;
 
-	assert(hash_size > 0);
-
 	n = get_var_int(&update_index, &in);
 	if (n < 0)
 		return n;
@@ -451,7 +446,7 @@ static int reftable_ref_record_is_deletion_void(const void *p)
 }
 
 static int reftable_ref_record_equal_void(const void *a,
-					  const void *b, int hash_size)
+					  const void *b, uint32_t hash_size)
 {
 	struct reftable_ref_record *ra = (struct reftable_ref_record *) a;
 	struct reftable_ref_record *rb = (struct reftable_ref_record *) b;
@@ -495,7 +490,7 @@ static void reftable_obj_record_release(void *rec)
 }
 
 static int reftable_obj_record_copy_from(void *rec, const void *src_rec,
-					 int hash_size UNUSED)
+					 uint32_t hash_size UNUSED)
 {
 	struct reftable_obj_record *obj = rec;
 	const struct reftable_obj_record *src = src_rec;
@@ -527,7 +522,7 @@ static uint8_t reftable_obj_record_val_type(const void *rec)
 }
 
 static int reftable_obj_record_encode(const void *rec, struct string_view s,
-				      int hash_size UNUSED)
+				      uint32_t hash_size UNUSED)
 {
 	const struct reftable_obj_record *r = rec;
 	struct string_view start = s;
@@ -562,7 +557,7 @@ static int reftable_obj_record_encode(const void *rec, struct string_view s,
 
 static int reftable_obj_record_decode(void *rec, struct reftable_buf key,
 				      uint8_t val_type, struct string_view in,
-				      int hash_size UNUSED,
+				      uint32_t hash_size UNUSED,
 				      struct reftable_buf *scratch UNUSED)
 {
 	struct string_view start = in;
@@ -626,7 +621,7 @@ static int not_a_deletion(const void *p UNUSED)
 }
 
 static int reftable_obj_record_equal_void(const void *a, const void *b,
-					  int hash_size UNUSED)
+					  uint32_t hash_size UNUSED)
 {
 	struct reftable_obj_record *ra = (struct reftable_obj_record *) a;
 	struct reftable_obj_record *rb = (struct reftable_obj_record *) b;
@@ -701,7 +696,7 @@ static int reftable_log_record_key(const void *r, struct reftable_buf *dest)
 }
 
 static int reftable_log_record_copy_from(void *rec, const void *src_rec,
-					 int hash_size)
+					 uint32_t hash_size)
 {
 	struct reftable_log_record *dst = rec;
 	const struct reftable_log_record *src =
@@ -782,7 +777,7 @@ static uint8_t reftable_log_record_val_type(const void *rec)
 }
 
 static int reftable_log_record_encode(const void *rec, struct string_view s,
-				      int hash_size)
+				      uint32_t hash_size)
 {
 	const struct reftable_log_record *r = rec;
 	struct string_view start = s;
@@ -830,7 +825,7 @@ static int reftable_log_record_encode(const void *rec, struct string_view s,
 
 static int reftable_log_record_decode(void *rec, struct reftable_buf key,
 				      uint8_t val_type, struct string_view in,
-				      int hash_size, struct reftable_buf *scratch)
+				      uint32_t hash_size, struct reftable_buf *scratch)
 {
 	struct string_view start = in;
 	struct reftable_log_record *r = rec;
@@ -978,7 +973,7 @@ static int null_streq(const char *a, const char *b)
 }
 
 static int reftable_log_record_equal_void(const void *a,
-					  const void *b, int hash_size)
+					  const void *b, uint32_t hash_size)
 {
 	return reftable_log_record_equal((struct reftable_log_record *) a,
 					 (struct reftable_log_record *) b,
@@ -1002,7 +997,7 @@ static int reftable_log_record_cmp_void(const void *_a, const void *_b)
 }
 
 int reftable_log_record_equal(const struct reftable_log_record *a,
-			      const struct reftable_log_record *b, int hash_size)
+			      const struct reftable_log_record *b, uint32_t hash_size)
 {
 	if (!(null_streq(a->refname, b->refname) &&
 	      a->update_index == b->update_index &&
@@ -1056,7 +1051,7 @@ static int reftable_index_record_key(const void *r, struct reftable_buf *dest)
 }
 
 static int reftable_index_record_copy_from(void *rec, const void *src_rec,
-					   int hash_size UNUSED)
+					   uint32_t hash_size UNUSED)
 {
 	struct reftable_index_record *dst = rec;
 	const struct reftable_index_record *src = src_rec;
@@ -1083,7 +1078,7 @@ static uint8_t reftable_index_record_val_type(const void *rec UNUSED)
 }
 
 static int reftable_index_record_encode(const void *rec, struct string_view out,
-					int hash_size UNUSED)
+					uint32_t hash_size UNUSED)
 {
 	const struct reftable_index_record *r =
 		(const struct reftable_index_record *)rec;
@@ -1101,7 +1096,7 @@ static int reftable_index_record_encode(const void *rec, struct string_view out,
 static int reftable_index_record_decode(void *rec, struct reftable_buf key,
 					uint8_t val_type UNUSED,
 					struct string_view in,
-					int hash_size UNUSED,
+					uint32_t hash_size UNUSED,
 					struct reftable_buf *scratch UNUSED)
 {
 	struct string_view start = in;
@@ -1122,7 +1117,7 @@ static int reftable_index_record_decode(void *rec, struct reftable_buf key,
 }
 
 static int reftable_index_record_equal(const void *a, const void *b,
-				       int hash_size UNUSED)
+				       uint32_t hash_size UNUSED)
 {
 	struct reftable_index_record *ia = (struct reftable_index_record *) a;
 	struct reftable_index_record *ib = (struct reftable_index_record *) b;
@@ -1156,14 +1151,14 @@ int reftable_record_key(struct reftable_record *rec, struct reftable_buf *dest)
 }
 
 int reftable_record_encode(struct reftable_record *rec, struct string_view dest,
-			   int hash_size)
+			   uint32_t hash_size)
 {
 	return reftable_record_vtable(rec)->encode(reftable_record_data(rec),
 						   dest, hash_size);
 }
 
 int reftable_record_copy_from(struct reftable_record *rec,
-			       struct reftable_record *src, int hash_size)
+			       struct reftable_record *src, uint32_t hash_size)
 {
 	assert(src->type == rec->type);
 
@@ -1178,7 +1173,7 @@ uint8_t reftable_record_val_type(struct reftable_record *rec)
 }
 
 int reftable_record_decode(struct reftable_record *rec, struct reftable_buf key,
-			   uint8_t extra, struct string_view src, int hash_size,
+			   uint8_t extra, struct string_view src, uint32_t hash_size,
 			   struct reftable_buf *scratch)
 {
 	return reftable_record_vtable(rec)->decode(reftable_record_data(rec),
@@ -1205,7 +1200,7 @@ int reftable_record_cmp(struct reftable_record *a, struct reftable_record *b)
 		reftable_record_data(a), reftable_record_data(b));
 }
 
-int reftable_record_equal(struct reftable_record *a, struct reftable_record *b, int hash_size)
+int reftable_record_equal(struct reftable_record *a, struct reftable_record *b, uint32_t hash_size)
 {
 	if (a->type != b->type)
 		return 0;
@@ -1213,7 +1208,7 @@ int reftable_record_equal(struct reftable_record *a, struct reftable_record *b,
 		reftable_record_data(a), reftable_record_data(b), hash_size);
 }
 
-static int hash_equal(const unsigned char *a, const unsigned char *b, int hash_size)
+static int hash_equal(const unsigned char *a, const unsigned char *b, uint32_t hash_size)
 {
 	if (a && b)
 		return !memcmp(a, b, hash_size);
@@ -1222,9 +1217,8 @@ static int hash_equal(const unsigned char *a, const unsigned char *b, int hash_s
 }
 
 int reftable_ref_record_equal(const struct reftable_ref_record *a,
-			      const struct reftable_ref_record *b, int hash_size)
+			      const struct reftable_ref_record *b, uint32_t hash_size)
 {
-	assert(hash_size > 0);
 	if (!null_streq(a->refname, b->refname))
 		return 0;
 
diff --git a/reftable/record.h b/reftable/record.h
index 0df950f401..c7755a4d75 100644
--- a/reftable/record.h
+++ b/reftable/record.h
@@ -47,18 +47,18 @@ struct reftable_record_vtable {
 	/* The record type of ('r' for ref). */
 	uint8_t type;
 
-	int (*copy_from)(void *dest, const void *src, int hash_size);
+	int (*copy_from)(void *dest, const void *src, uint32_t hash_size);
 
 	/* a value of [0..7], indicating record subvariants (eg. ref vs. symref
 	 * vs ref deletion) */
 	uint8_t (*val_type)(const void *rec);
 
 	/* encodes rec into dest, returning how much space was used. */
-	int (*encode)(const void *rec, struct string_view dest, int hash_size);
+	int (*encode)(const void *rec, struct string_view dest, uint32_t hash_size);
 
 	/* decode data from `src` into the record. */
 	int (*decode)(void *rec, struct reftable_buf key, uint8_t extra,
-		      struct string_view src, int hash_size,
+		      struct string_view src, uint32_t hash_size,
 		      struct reftable_buf *scratch);
 
 	/* deallocate and null the record. */
@@ -68,7 +68,7 @@ struct reftable_record_vtable {
 	int (*is_deletion)(const void *rec);
 
 	/* Are two records equal? This assumes they have the same type. Returns 0 for non-equal. */
-	int (*equal)(const void *a, const void *b, int hash_size);
+	int (*equal)(const void *a, const void *b, uint32_t hash_size);
 
 	/*
 	 * Compare keys of two records with each other. The records must have
@@ -135,16 +135,16 @@ void reftable_record_init(struct reftable_record *rec, uint8_t typ);
 
 /* see struct record_vtable */
 int reftable_record_cmp(struct reftable_record *a, struct reftable_record *b);
-int reftable_record_equal(struct reftable_record *a, struct reftable_record *b, int hash_size);
+int reftable_record_equal(struct reftable_record *a, struct reftable_record *b, uint32_t hash_size);
 int reftable_record_key(struct reftable_record *rec, struct reftable_buf *dest);
 int reftable_record_copy_from(struct reftable_record *rec,
-			      struct reftable_record *src, int hash_size);
+			      struct reftable_record *src, uint32_t hash_size);
 uint8_t reftable_record_val_type(struct reftable_record *rec);
 int reftable_record_encode(struct reftable_record *rec, struct string_view dest,
-			   int hash_size);
+			   uint32_t hash_size);
 int reftable_record_decode(struct reftable_record *rec, struct reftable_buf key,
 			   uint8_t extra, struct string_view src,
-			   int hash_size, struct reftable_buf *scratch);
+			   uint32_t hash_size, struct reftable_buf *scratch);
 int reftable_record_is_deletion(struct reftable_record *rec);
 
 static inline uint8_t reftable_record_type(struct reftable_record *rec)
diff --git a/reftable/reftable-record.h b/reftable/reftable-record.h
index ddd48eb579..931e594744 100644
--- a/reftable/reftable-record.h
+++ b/reftable/reftable-record.h
@@ -65,7 +65,7 @@ void reftable_ref_record_release(struct reftable_ref_record *ref);
 
 /* returns whether two reftable_ref_records are the same. Useful for testing. */
 int reftable_ref_record_equal(const struct reftable_ref_record *a,
-			      const struct reftable_ref_record *b, int hash_size);
+			      const struct reftable_ref_record *b, uint32_t hash_size);
 
 /* reftable_log_record holds a reflog entry */
 struct reftable_log_record {
@@ -105,6 +105,6 @@ void reftable_log_record_release(struct reftable_log_record *log);
 
 /* returns whether two records are equal. Useful for testing. */
 int reftable_log_record_equal(const struct reftable_log_record *a,
-			      const struct reftable_log_record *b, int hash_size);
+			      const struct reftable_log_record *b, uint32_t hash_size);
 
 #endif
diff --git a/t/unit-tests/t-reftable-record.c b/t/unit-tests/t-reftable-record.c
index 6d912b9c8f..d49d2a2729 100644
--- a/t/unit-tests/t-reftable-record.c
+++ b/t/unit-tests/t-reftable-record.c
@@ -76,7 +76,7 @@ static void t_varint_overflow(void)
 
 static void set_hash(uint8_t *h, int j)
 {
-	for (int i = 0; i < hash_size(REFTABLE_HASH_SHA1); i++)
+	for (size_t i = 0; i < hash_size(REFTABLE_HASH_SHA1); i++)
 		h[i] = (j >> i) & 0xff;
 }