diff --git a/builtin/replace.c b/builtin/replace.c
index aed6b2c8de..b85681080d 100644
--- a/builtin/replace.c
+++ b/builtin/replace.c
@@ -459,7 +459,7 @@ static int create_graft(int argc, const char **argv, int force, int gentle)
 	struct commit *commit;
 	struct strbuf buf = STRBUF_INIT;
 	const char *buffer;
-	unsigned long size;
+	size_t size;
 
 	if (repo_get_oid(the_repository, old_ref, &old_oid) < 0)
 		return error(_("not a valid object name: '%s'"), old_ref);
diff --git a/builtin/stash.c b/builtin/stash.c
index c4809f299a..83fecc4a7f 100644
--- a/builtin/stash.c
+++ b/builtin/stash.c
@@ -2083,7 +2083,7 @@ static int write_commit_with_parents(struct repository *r,
 	const char *orig_author, *orig_committer;
 	char *author = NULL, *committer = NULL;
 	const char *buffer;
-	unsigned long bufsize;
+	size_t bufsize;
 	const char *p;
 	struct strbuf msg = STRBUF_INIT;
 	int ret = 0;
@@ -2135,7 +2135,7 @@ static int do_import_stash(struct repository *r, const char *rev)
 	struct object_id chain;
 	int res = 0;
 	const char *buffer = NULL;
-	unsigned long bufsize;
+	size_t bufsize;
 	struct commit *this = NULL;
 	struct commit_list *items = NULL, *cur;
 	char *msg = NULL;
diff --git a/commit.c b/commit.c
index 5c4a4319b5..f0aade5b60 100644
--- a/commit.c
+++ b/commit.c
@@ -349,7 +349,7 @@ int for_each_commit_graft(each_commit_graft_fn fn, void *cb_data)
 
 struct commit_buffer {
 	void *buffer;
-	unsigned long size;
+	size_t size;
 };
 define_commit_slab(buffer_slab, struct commit_buffer);
 
@@ -366,7 +366,8 @@ void free_commit_buffer_slab(struct buffer_slab *bs)
 	free(bs);
 }
 
-void set_commit_buffer(struct repository *r, struct commit *commit, void *buffer, unsigned long size)
+void set_commit_buffer(struct repository *r, struct commit *commit,
+		       void *buffer, size_t size)
 {
 	struct commit_buffer *v = buffer_slab_at(
 		r->parsed_objects->buffer_slab, commit);
@@ -374,7 +375,9 @@ void set_commit_buffer(struct repository *r, struct commit *commit, void *buffer
 	v->size = size;
 }
 
-const void *get_cached_commit_buffer(struct repository *r, const struct commit *commit, unsigned long *sizep)
+const void *get_cached_commit_buffer(struct repository *r,
+				     const struct commit *commit,
+				     size_t *sizep)
 {
 	struct commit_buffer *v = buffer_slab_peek(
 		r->parsed_objects->buffer_slab, commit);
@@ -390,7 +393,7 @@ const void *get_cached_commit_buffer(struct repository *r, const struct commit *
 
 const void *repo_get_commit_buffer(struct repository *r,
 				   const struct commit *commit,
-				   unsigned long *sizep)
+				   size_t *sizep)
 {
 	const void *ret = get_cached_commit_buffer(r, commit, sizep);
 	if (!ret) {
@@ -404,7 +407,7 @@ const void *repo_get_commit_buffer(struct repository *r,
 			die("expected commit for %s, got %s",
 			    oid_to_hex(&commit->object.oid), type_name(type));
 		if (sizep)
-			*sizep = cast_size_t_to_ulong(size);
+			*sizep = size;
 	}
 	return ret;
 }
@@ -1192,7 +1195,7 @@ int parse_signed_commit(const struct commit *commit,
 			struct strbuf *payload, struct strbuf *signature,
 			const struct git_hash_algo *algop)
 {
-	unsigned long size;
+	size_t size;
 	const char *buffer = repo_get_commit_buffer(the_repository, commit,
 						    &size);
 	int ret = parse_buffer_signed_by_header(buffer, size, payload, signature, algop);
@@ -1365,7 +1368,7 @@ int verify_commit_buffer(const char *buffer, size_t size,
 
 int check_commit_signature(const struct commit *commit, struct signature_check *sigc)
 {
-	unsigned long size;
+	size_t size;
 	const char *buffer = repo_get_commit_buffer(the_repository, commit, &size);
 	int ret = verify_commit_buffer(buffer, size, sigc);
 
@@ -1462,7 +1465,7 @@ struct commit_extra_header *read_commit_extra_headers(struct commit *commit,
 						      const char **exclude)
 {
 	struct commit_extra_header *extra = NULL;
-	unsigned long size;
+	size_t size;
 	const char *buffer = repo_get_commit_buffer(the_repository, commit,
 						    &size);
 	extra = read_commit_extra_header_lines(buffer, size, exclude);
diff --git a/commit.h b/commit.h
index 1061ed791b..97779ec943 100644
--- a/commit.h
+++ b/commit.h
@@ -131,13 +131,15 @@ void free_commit_buffer_slab(struct buffer_slab *bs);
  * Associate an object buffer with the commit. The ownership of the
  * memory is handed over to the commit, and must be free()-able.
  */
-void set_commit_buffer(struct repository *r, struct commit *, void *buffer, unsigned long size);
+void set_commit_buffer(struct repository *r, struct commit *,
+		       void *buffer, size_t size);
 
 /*
  * Get any cached object buffer associated with the commit. Returns NULL
  * if none. The resulting memory should not be freed.
  */
-const void *get_cached_commit_buffer(struct repository *, const struct commit *, unsigned long *size);
+const void *get_cached_commit_buffer(struct repository *,
+				     const struct commit *, size_t *size);
 
 /*
  * Get the commit's object contents, either from cache or by reading the object
@@ -146,7 +148,7 @@ const void *get_cached_commit_buffer(struct repository *, const struct commit *,
  */
 const void *repo_get_commit_buffer(struct repository *r,
 				   const struct commit *,
-				   unsigned long *size);
+				   size_t *size);
 
 /*
  * Tell the commit subsystem that we are done with a particular commit buffer.