diff --git a/csum-file.h b/csum-file.h
index f9cbd317fb..e54d53d1d0 100644
--- a/csum-file.h
+++ b/csum-file.h
@@ -62,4 +62,11 @@ static inline void hashwrite_be32(struct hashfile *f, uint32_t data)
 	hashwrite(f, &data, sizeof(data));
 }
 
+static inline size_t hashwrite_be64(struct hashfile *f, uint64_t data)
+{
+	data = htonll(data);
+	hashwrite(f, &data, sizeof(data));
+	return sizeof(data);
+}
+
 #endif
diff --git a/midx.c b/midx.c
index d233b54ac7..da03c1449a 100644
--- a/midx.c
+++ b/midx.c
@@ -785,9 +785,7 @@ static size_t write_midx_large_offsets(struct hashfile *f, uint32_t nr_large_off
 		if (!(offset >> 31))
 			continue;
 
-		hashwrite_be32(f, offset >> 32);
-		hashwrite_be32(f, offset & 0xffffffffUL);
-		written += 2 * sizeof(uint32_t);
+		written += hashwrite_be64(f, offset);
 
 		nr_large_offset--;
 	}
@@ -975,8 +973,7 @@ static int write_midx_internal(const char *object_dir, struct multi_pack_index *
 			    chunk_offsets[i]);
 
 		hashwrite_be32(f, chunk_ids[i]);
-		hashwrite_be32(f, chunk_offsets[i] >> 32);
-		hashwrite_be32(f, chunk_offsets[i]);
+		hashwrite_be64(f, chunk_offsets[i]);
 
 		written += MIDX_CHUNKLOOKUP_WIDTH;
 	}
diff --git a/pack-write.c b/pack-write.c
index 23e19cc1ec..3513665e1e 100644
--- a/pack-write.c
+++ b/pack-write.c
@@ -151,13 +151,10 @@ const char *write_idx_file(const char *index_name, struct pack_idx_entry **objec
 		while (nr_large_offset) {
 			struct pack_idx_entry *obj = *list++;
 			uint64_t offset = obj->offset;
-			uint32_t split[2];
 
 			if (!need_large_offset(offset, opts))
 				continue;
-			split[0] = htonl(offset >> 32);
-			split[1] = htonl(offset & 0xffffffff);
-			hashwrite(f, split, 8);
+			hashwrite_be64(f, offset);
 			nr_large_offset--;
 		}
 	}