diff --git a/src/util/virrandom.c b/src/util/virrandom.c
index 630bc003af1360e8d3293da6f463d7efb518eaa4..151cf4bda8d9e73a23afa517a73a17ae98d729b6 100644
--- a/src/util/virrandom.c
+++ b/src/util/virrandom.c
@@ -123,8 +123,8 @@ virRandomGenerateWWN(char **wwn,
         return -1;
     }
 
-    if (virAsprintf(wwn, "5" "%s%09" PRIx64,
-                    oui, virRandomBits(36)) < 0) {
+    if (virAsprintf(wwn, "5" "%s%09llx", oui,
+                    (unsigned long long)virRandomBits(36)) < 0) {
         virReportOOMError();
         return -1;
     }