diff -r f2cdbf31ce9b source/lib/sysdep/arch/x86_x64/topology.cpp
--- source/lib/sysdep/arch/x86_x64/topology.cpp	Sat Jul 10 18:42:54 2010 +0100
+++ source/lib/sysdep/arch/x86_x64/topology.cpp	Sat Jul 24 22:34:51 2010 +0100
@@ -137,18 +137,24 @@
 // core, package and shared cache. if they are available, we can determine
 // the exact topology; otherwise we have to guess.
 
-// side effect: `removes' (via std::unique) duplicate IDs.
-static bool AreApicIdsUnique(u8* apicIds, size_t numProcessors)
+// if false is returned, the APIC IDs are fishy and shouldn't be used.
+// side effect: sorts IDs and `removes' (via std::unique) duplicates.
+static bool AreApicIdsUnique(u8* apicIds, size_t numIds)
 {
-	u8* const end = std::unique(apicIds, apicIds+numProcessors);
-	const size_t numIds = end-apicIds;
-	if(numIds == numProcessors)	// all unique
+	std::sort(apicIds, apicIds+numIds);
+	u8* const end = std::unique(apicIds, apicIds+numIds);
+	const size_t numUnique = end-apicIds;
+	// all unique => IDs are valid.
+	if(numUnique == numIds)
 		return true;
 
-	// the only legitimate cause of duplication is when no xAPIC is
-	// present (i.e. all are 0)
-	debug_assert(numIds == 1);
-	debug_assert(apicIds[0] == 0);
+	// all zero => the system lacks an xAPIC.
+	if(numUnique == 1 && apicIds[0] == 0)
+		return false;
+
+	// duplicated IDs => something went wrong. for example, VMs might not
+	// expose all physical processors, and OS X still doesn't support
+	// thread affinity masks.
 	return false;
 }
 
@@ -245,7 +251,8 @@
 
 		// assume cores are enabled and count as processors.
 		const size_t numPackagesTimesLogical = os_cpu_NumProcessors() / CoresPerPackage();
-		debug_assert(numPackagesTimesLogical != 0);
+		// note: this might give numPackagesTimesLogical == 0 (e.g. when running in some VMs)
+
 		// assume hyperthreads are enabled.
 		size_t numPackages = numPackagesTimesLogical;
 		// if they are reported as processors, remove them from the count.