diff --git a/builtin/unpack-objects.c b/builtin/unpack-objects.c
index c3d0fc7507..842db7c120 100644
--- a/builtin/unpack-objects.c
+++ b/builtin/unpack-objects.c
@@ -40,7 +40,7 @@ static struct progress *progress;
  */
 struct obj_buffer {
 	char *buffer;
-	unsigned long size;
+	size_t size;
 };
 
 static struct decoration obj_decorate;
@@ -50,7 +50,7 @@ static struct obj_buffer *lookup_object_buffer(struct object *base)
 	return lookup_decoration(&obj_decorate, base);
 }
 
-static void add_object_buffer(struct object *object, char *buffer, unsigned long size)
+static void add_object_buffer(struct object *object, char *buffer, size_t size)
 {
 	struct obj_buffer *obj;
 	CALLOC_ARRAY(obj, 1);
@@ -114,10 +114,10 @@ static void use(int bytes)
  * allocated buffer which is reused to hold temporary zstream output
  * and return NULL instead of returning garbage data.
  */
-static void *get_data(unsigned long size)
+static void *get_data(size_t size)
 {
 	git_zstream stream;
-	unsigned long bufsize = dry_run && size > 8192 ? 8192 : size;
+	size_t bufsize = dry_run && size > 8192 ? 8192 : size;
 	void *buf = xmallocz(bufsize);
 
 	memset(&stream, 0, sizeof(stream));
@@ -161,7 +161,7 @@ struct delta_info {
 	struct object_id base_oid;
 	unsigned nr;
 	off_t base_offset;
-	unsigned long size;
+	size_t size;
 	void *delta;
 	struct delta_info *next;
 };
@@ -170,7 +170,7 @@ static struct delta_info *delta_list;
 
 static void add_delta_to_list(unsigned nr, const struct object_id *base_oid,
 			      off_t base_offset,
-			      void *delta, unsigned long size)
+			      void *delta, size_t size)
 {
 	struct delta_info *info = xmalloc(sizeof(*info));
 
@@ -261,7 +261,7 @@ static void write_rest(void)
 }
 
 static void added_object(unsigned nr, enum object_type type,
-			 void *data, unsigned long size);
+			 void *data, size_t size);
 
 /*
  * Write out nr-th object from the list, now we know the contents
@@ -269,7 +269,7 @@ static void added_object(unsigned nr, enum object_type type,
  * to be checked at the end.
  */
 static void write_object(unsigned nr, enum object_type type,
-			 void *buf, unsigned long size)
+			 void *buf, size_t size)
 {
 	if (!strict) {
 		if (odb_write_object(the_repository->objects, buf, size, type,
@@ -310,8 +310,8 @@ static void write_object(unsigned nr, enum object_type type,
 }
 
 static void resolve_delta(unsigned nr, enum object_type type,
-			  void *base, unsigned long base_size,
-			  void *delta, unsigned long delta_size)
+			  void *base, size_t base_size,
+			  void *delta, size_t delta_size)
 {
 	void *result;
 	size_t result_size;
@@ -330,7 +330,7 @@ static void resolve_delta(unsigned nr, enum object_type type,
  * resolve all the deltified objects that are based on it.
  */
 static void added_object(unsigned nr, enum object_type type,
-			 void *data, unsigned long size)
+			 void *data, size_t size)
 {
 	struct delta_info **p = &delta_list;
 	struct delta_info *info;
@@ -349,7 +349,7 @@ static void added_object(unsigned nr, enum object_type type,
 	}
 }
 
-static void unpack_non_delta_entry(enum object_type type, unsigned long size,
+static void unpack_non_delta_entry(enum object_type type, size_t size,
 				   unsigned nr)
 {
 	void *buf = get_data(size);
@@ -385,7 +385,7 @@ static ssize_t feed_input_zstream(struct odb_write_stream *in_stream,
 	return buf_len - zstream->avail_out;
 }
 
-static void stream_blob(unsigned long size, unsigned nr)
+static void stream_blob(size_t size, unsigned nr)
 {
 	git_zstream zstream = { 0 };
 	struct input_zstream_data data = { 0 };
@@ -416,7 +416,7 @@ static void stream_blob(unsigned long size, unsigned nr)
 }
 
 static int resolve_against_held(unsigned nr, const struct object_id *base,
-				void *delta_data, unsigned long delta_size)
+				void *delta_data, size_t delta_size)
 {
 	struct object *obj;
 	struct obj_buffer *obj_buffer;
@@ -431,12 +431,11 @@ static int resolve_against_held(unsigned nr, const struct object_id *base,
 	return 1;
 }
 
-static void unpack_delta_entry(enum object_type type, unsigned long delta_size,
+static void unpack_delta_entry(enum object_type type, size_t delta_size,
 			       unsigned nr)
 {
 	void *delta_data, *base;
-	unsigned long base_size;
-	size_t base_size_st = 0;
+	size_t base_size;
 	struct object_id base_oid;
 
 	if (type == OBJ_REF_DELTA) {
@@ -513,8 +512,7 @@ static void unpack_delta_entry(enum object_type type, unsigned long delta_size,
 		return;
 
 	base = odb_read_object(the_repository->objects, &base_oid,
-			       &type, &base_size_st);
-	base_size = cast_size_t_to_ulong(base_size_st);
+			       &type, &base_size);
 	if (!base) {
 		error("failed to read delta-pack base object %s",
 		      oid_to_hex(&base_oid));