diff --git a/hw/isa/isa-bus.c b/hw/isa/isa-bus.c
index ce9999f7f7..b3d2e5ec52 100644
--- a/hw/isa/isa-bus.c
+++ b/hw/isa/isa-bus.c
@@ -114,7 +114,7 @@ static inline void isa_init_ioport(ISADevice *dev, uint16_t ioport)
 
 void isa_register_ioport(ISADevice *dev, MemoryRegion *io, uint16_t start)
 {
-    memory_region_add_subregion(isabus->address_space_io, start, io);
+    memory_region_add_subregion(isa_address_space_io(dev), start, io);
     isa_init_ioport(dev, start);
 }
 
@@ -135,7 +135,7 @@ int isa_register_portio_list(ISADevice *dev,
     isa_init_ioport(dev, start);
 
     portio_list_init(piolist, OBJECT(dev), pio_start, opaque, name);
-    portio_list_add(piolist, isabus->address_space_io, start);
+    portio_list_add(piolist, isa_address_space_io(dev), start);
 
     return 0;
 }