diff --git a/util/cutils.c b/util/cutils.c
index e098debdc0..d682c90901 100644
--- a/util/cutils.c
+++ b/util/cutils.c
@@ -825,7 +825,7 @@ const char *qemu_ether_ntoa(const MACAddr *mac)
 char *size_to_str(uint64_t val)
 {
     static const char *suffixes[] = { "", "Ki", "Mi", "Gi", "Ti", "Pi", "Ei" };
-    unsigned long div;
+    uint64_t div;
     int i;
 
     /*