diff --git a/tools/ab_test.py b/tools/ab_test.py
index 470a1ef16ff..7f44064ffde 100755
--- a/tools/ab_test.py
+++ b/tools/ab_test.py
@@ -53,8 +53,8 @@
     # boot time metrics
     {"performance_test": "test_boottime", "metric": "resume_time"},
     # block throughput on m8g
-    {"fio_engine": "libaio", "vcpus": 2, "instance": "m8g.metal-24xl"},
-    {"fio_engine": "libaio", "vcpus": 2, "instance": "m8g.metal-48xl"},
+    {"fio_engine": "libaio", "vcpus": "2", "instance": "m8g.metal-24xl"},
+    {"fio_engine": "libaio", "vcpus": "2", "instance": "m8g.metal-48xl"},
 ]