diff --git a/block/blkio.c b/block/blkio.c
index 0a0a6c0f5f..bc2f21784c 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;