diff --git a/hw/ppc/spapr.c b/hw/ppc/spapr.c
index c92d269027..bcb0e184a0 100644
--- a/hw/ppc/spapr.c
+++ b/hw/ppc/spapr.c
@@ -2863,7 +2863,13 @@ static void spapr_core_pre_plug(HotplugHandler *hotplug_dev, DeviceState *dev,
         goto out;
     }
 
-    if (cc->nr_threads != smp_threads) {
+    /*
+     * In general we should have homogeneous threads-per-core, but old
+     * (pre hotplug support) machine types allow the last core to have
+     * reduced threads as a compatibility hack for when we allowed
+     * total vcpus not a multiple of threads-per-core.
+     */
+    if (mc->has_hotpluggable_cpus && (cc->nr_threads != smp_threads)) {
         error_setg(errp, "invalid nr-threads %d, must be %d",
                    cc->nr_threads, smp_threads);
         return;