diff --git a/hw/watchdog/wdt_aspeed.c b/hw/watchdog/wdt_aspeed.c
index 958725a1b5..eefca31ae4 100644
--- a/hw/watchdog/wdt_aspeed.c
+++ b/hw/watchdog/wdt_aspeed.c
@@ -260,6 +260,7 @@ static void aspeed_wdt_realize(DeviceState *dev, Error **errp)
 {
     SysBusDevice *sbd = SYS_BUS_DEVICE(dev);
     AspeedWDTState *s = ASPEED_WDT(dev);
+    AspeedWDTClass *awc = ASPEED_WDT_GET_CLASS(dev);
 
     assert(s->scu);
 
@@ -271,7 +272,7 @@ static void aspeed_wdt_realize(DeviceState *dev, Error **errp)
     s->pclk_freq = PCLK_HZ;
 
     memory_region_init_io(&s->iomem, OBJECT(s), &aspeed_wdt_ops, s,
-                          TYPE_ASPEED_WDT, ASPEED_WDT_REGS_MAX * 4);
+                          TYPE_ASPEED_WDT, awc->iosize);
     sysbus_init_mmio(sbd, &s->iomem);
 }