diff --git a/builtin/pack-objects.c b/builtin/pack-objects.c
index 7e35d0da4c..037ae4d727 100644
--- a/builtin/pack-objects.c
+++ b/builtin/pack-objects.c
@@ -2259,8 +2259,7 @@ static void check_object(struct object_entry *entry, uint32_t object_index)
 		int have_base = 0;
 		struct object_id base_ref;
 		struct object_entry *base_entry;
-		unsigned long used, used_0;
-		size_t avail;
+		size_t used, used_0, avail;
 		off_t ofs;
 		unsigned char *buf, c;
 		enum object_type type;
@@ -2756,8 +2755,7 @@ size_t oe_get_size_slow(struct packing_data *pack,
 	struct pack_window *w_curs;
 	unsigned char *buf;
 	enum object_type type;
-	unsigned long used;
-	size_t avail, size;
+	size_t used, avail, size;
 
 	if (e->type_ != OBJ_OFS_DELTA && e->type_ != OBJ_REF_DELTA) {
 		size_t sz;
diff --git a/oss-fuzz/fuzz-pack-headers.c b/oss-fuzz/fuzz-pack-headers.c
index ef61ab577c..e44afe0b8d 100644
--- a/oss-fuzz/fuzz-pack-headers.c
+++ b/oss-fuzz/fuzz-pack-headers.c
@@ -9,7 +9,7 @@ int LLVMFuzzerTestOneInput(const uint8_t *data, size_t size)
 	size_t len;
 
 	unpack_object_header_buffer((const unsigned char *)data,
-				    (unsigned long)size, &type, &len);
+				    size, &type, &len);
 
 	return 0;
 }
diff --git a/packfile.c b/packfile.c
index 7fbe47ca18..59d0c83c40 100644
--- a/packfile.c
+++ b/packfile.c
@@ -1134,12 +1134,11 @@ out:
 	return ret;
 }
 
-unsigned long unpack_object_header_buffer(const unsigned char *buf,
-		unsigned long len, enum object_type *type, size_t *sizep)
+size_t unpack_object_header_buffer(const unsigned char *buf, size_t len,
+				   enum object_type *type, size_t *sizep)
 {
 	unsigned shift;
-	size_t size, c;
-	unsigned long used = 0;
+	size_t size, c, used = 0;
 
 	c = buf[used++];
 	*type = (c >> 4) & 7;
@@ -1228,8 +1227,7 @@ int unpack_object_header(struct packed_git *p,
 			 size_t *sizep)
 {
 	unsigned char *base;
-	size_t left;
-	unsigned long used;
+	size_t left, used;
 	enum object_type type;
 
 	/* use_pack() assures us we have [base, base + 20) available
diff --git a/packfile.h b/packfile.h
index 820d247d05..dcf1152644 100644
--- a/packfile.h
+++ b/packfile.h
@@ -458,7 +458,8 @@ off_t find_pack_entry_one(const struct object_id *oid, struct packed_git *);
 int is_pack_valid(struct packed_git *);
 void *unpack_entry(struct repository *r, struct packed_git *, off_t,
 		   enum object_type *, size_t *);
-unsigned long unpack_object_header_buffer(const unsigned char *buf, unsigned long len, enum object_type *type, size_t *sizep);
+size_t unpack_object_header_buffer(const unsigned char *buf, size_t len,
+				   enum object_type *type, size_t *sizep);
 size_t get_size_from_delta(struct packed_git *, struct pack_window **, off_t);
 int unpack_object_header(struct packed_git *, struct pack_window **, off_t *, size_t *);
 off_t get_delta_base(struct packed_git *p, struct pack_window **w_curs,