diff --git a/hw/arm/vexpress.c b/hw/arm/vexpress.c
index f1b4524..1a14c19 100644
--- a/hw/arm/vexpress.c
+++ b/hw/arm/vexpress.c
@@ -783,22 +783,30 @@
 
 static void vexpress_a9_class_init(ObjectClass *oc, void *data)
 {
+    static const char * const valid_cpu_types[] = {
+        ARM_CPU_TYPE_NAME("cortex-a9"),
+        NULL
+    };
     MachineClass *mc = MACHINE_CLASS(oc);
     VexpressMachineClass *vmc = VEXPRESS_MACHINE_CLASS(oc);
 
     mc->desc = "ARM Versatile Express for Cortex-A9";
-    mc->default_cpu_type = ARM_CPU_TYPE_NAME("cortex-a9");
+    mc->valid_cpu_types = valid_cpu_types;
 
     vmc->daughterboard = &a9_daughterboard;
 }
 
 static void vexpress_a15_class_init(ObjectClass *oc, void *data)
 {
+    static const char * const valid_cpu_types[] = {
+        ARM_CPU_TYPE_NAME("cortex-a15"),
+        NULL
+    };
     MachineClass *mc = MACHINE_CLASS(oc);
     VexpressMachineClass *vmc = VEXPRESS_MACHINE_CLASS(oc);
 
     mc->desc = "ARM Versatile Express for Cortex-A15";
-    mc->default_cpu_type = ARM_CPU_TYPE_NAME("cortex-a15");
+    mc->valid_cpu_types = valid_cpu_types;
 
     vmc->daughterboard = &a15_daughterboard;