diff --git a/hw/qdev.c b/hw/qdev.c
index 479eb72..00a20a8 100644
--- a/hw/qdev.c
+++ b/hw/qdev.c
@@ -503,7 +503,7 @@ BusState *qbus_create(BusInfo *info, DeviceState *parent, const char *name)
         len = snprintf(buf, len, "%s.%d", info->name,
                        parent ? parent->num_child_bus : 0);
         for (i = 0; i < len; i++)
-            buf[i] = tolower(buf[i]);
+            buf[i] = qemu_tolower(buf[i]);
         bus->name = buf;
     }