diff --git a/qemu/tests/cfg/block_hotplug.cfg b/qemu/tests/cfg/block_hotplug.cfg
index 643f7958105b3a371d627c76d2cad0a5d3826890..f33fe26d432840f69c87a385c359e5f4d746086c 100644
--- a/qemu/tests/cfg/block_hotplug.cfg
+++ b/qemu/tests/cfg/block_hotplug.cfg
@@ -64,7 +64,7 @@
             only with_plug
             only one_pci
             sub_type_after_plug = block_resize
-            blk_extra_params_stg0 += " serial=TARGET_DISK0"
+            blk_extra_params_stg0 += ",serial=TARGET_DISK0"
             block_size_cmd = "fdisk -l | grep {0}"
             block_size_pattern = ",\s+(\d+\s+b)ytes"
             disk_change_ratio = "1.5 0.5"