Index: ps/trunk/source/lib/sysdep/arch/x86_x64/apic.h
===================================================================
--- ps/trunk/source/lib/sysdep/arch/x86_x64/apic.h
+++ ps/trunk/source/lib/sysdep/arch/x86_x64/apic.h
@@ -40,6 +40,9 @@
 // apicId<->contiguousId and apicId<->processor.
 LIB_API bool AreApicIdsReliable();
 
+// we may get the apicId of a processor we don't have access to.
+LIB_API bool IsProcessorKnown(ApicId apicId);
+
 LIB_API size_t ProcessorFromApicId(ApicId apicId);
 LIB_API size_t ContiguousIdFromApicId(ApicId apicId);
 
Index: ps/trunk/source/lib/sysdep/arch/x86_x64/apic.cpp
===================================================================
--- ps/trunk/source/lib/sysdep/arch/x86_x64/apic.cpp
+++ ps/trunk/source/lib/sysdep/arch/x86_x64/apic.cpp
@@ -1,4 +1,4 @@
-/* Copyright (C) 2011 Wildfire Games.
+/* Copyright (C) 2020 Wildfire Games.
  *
  * Permission is hereby granted, free of charge, to any person obtaining
  * a copy of this software and associated documentation files (the
@@ -110,6 +110,13 @@
 	return true;
 }
 
+bool IsProcessorKnown(ApicId apicId)
+{
+	ModuleInit(&apicInitState, InitApicIds);
+
+	const ApicId* pos = std::find(processorApicIds, processorApicIds+numIds, apicId);
+	return pos != processorApicIds+numIds;
+}
 
 static size_t IndexFromApicId(const ApicId* apicIds, ApicId apicId)
 {
Index: ps/trunk/source/lib/sysdep/os/win/wnuma.cpp
===================================================================
--- ps/trunk/source/lib/sysdep/os/win/wnuma.cpp
+++ ps/trunk/source/lib/sysdep/os/win/wnuma.cpp
@@ -1,4 +1,4 @@
-/* Copyright (C) 2018 Wildfire Games.
+/* Copyright (C) 2020 Wildfire Games.
  *
  * Permission is hereby granted, free of charge, to any person obtaining
  * a copy of this software and associated documentation files (the
@@ -232,13 +232,19 @@
 		header = (const AffinityHeader*)(uintptr_t(header) + header->length))
 	{
 		const AffinityAPIC* affinityAPIC = DynamicCastFromHeader<AffinityAPIC>(header);
-		if(affinityAPIC)
+		if(!affinityAPIC)
+			continue;
+
+		if(!IsProcessorKnown(affinityAPIC->apicId))
 		{
-			const size_t processor = ProcessorFromApicId(affinityAPIC->apicId);
-			const u32 proximityDomainNumber = affinityAPIC->ProximityDomainNumber();
-			ProximityDomain& proximityDomain = proximityDomains[proximityDomainNumber];
-			proximityDomain.processorMask |= Bit<uintptr_t>(processor);
+			debug_printf("Processor with APIC ID %d found in SRAT but not known to CPUID.", affinityAPIC->apicId);
+			continue;
 		}
+
+		const size_t processor = ProcessorFromApicId(affinityAPIC->apicId);
+		const u32 proximityDomainNumber = affinityAPIC->ProximityDomainNumber();
+		ProximityDomain& proximityDomain = proximityDomains[proximityDomainNumber];
+		proximityDomain.processorMask |= Bit<uintptr_t>(processor);
 	}
 
 	return proximityDomains;