diff --git a/hw/char/serial.c b/hw/char/serial.c
index 7746dfcee8..6c327183c7 100644
--- a/hw/char/serial.c
+++ b/hw/char/serial.c
@@ -998,6 +998,7 @@ static void serial_io_realize(DeviceState *dev, Error **errp)
     }
 
     memory_region_init_io(&s->io, NULL, &serial_io_ops, s, "serial", 8);
+    sysbus_init_mmio(SYS_BUS_DEVICE(sio), &s->io);
     sysbus_init_irq(SYS_BUS_DEVICE(sio), &s->irq);
 }
 
diff --git a/hw/mips/mips_mipssim.c b/hw/mips/mips_mipssim.c
index 2c2c7f25b2..84c03dd035 100644
--- a/hw/mips/mips_mipssim.c
+++ b/hw/mips/mips_mipssim.c
@@ -227,7 +227,8 @@ mips_mipssim_init(MachineState *machine)
         qdev_set_legacy_instance_id(dev, 0x3f8, 2);
         qdev_init_nofail(dev);
         sysbus_connect_irq(SYS_BUS_DEVICE(dev), 0, env->irq[4]);
-        sysbus_add_io(SYS_BUS_DEVICE(dev), 0x3f8, &SERIAL_IO(dev)->serial.io);
+        sysbus_add_io(SYS_BUS_DEVICE(dev), 0x3f8,
+                      sysbus_mmio_get_region(SYS_BUS_DEVICE(dev), 0));
     }
 
     if (nd_table[0].used)