diff --git a/block/blkio.c b/block/blkio.c
index 027c16ceb6c42562cb3867353adfa7008c06782b..52ac94527fb4c788424345d1823d2ad50f88fb6d 100644
--- a/block/blkio.c
+++ b/block/blkio.c
@@ -68,7 +68,7 @@ typedef struct {
     CoQueue bounce_available;
 
     /* The value of the "mem-region-alignment" property */
-    size_t mem_region_alignment;
+    uint64_t mem_region_alignment;
 
     /* Can we skip adding/deleting blkio_mem_regions? */
     bool needs_mem_regions;