diff --git a/fs/buffer.c b/fs/buffer.c
index f23bb64..e999472 100644
--- a/fs/buffer.c
+++ b/fs/buffer.c
@@ -2598,7 +2598,7 @@
 	unsigned offset = from & (PAGE_CACHE_SIZE-1);
 	unsigned to;
 	struct page *page;
-	struct address_space_operations *a_ops = mapping->a_ops;
+	const struct address_space_operations *a_ops = mapping->a_ops;
 	char *kaddr;
 	int ret = 0;