diff --git a/PerfectNumbers.Core/MersenneDivisorCycles.cs b/PerfectNumbers.Core/MersenneDivisorCycles.cs
index bfcd972..afa8d70 100644
--- a/PerfectNumbers.Core/MersenneDivisorCycles.cs
+++ b/PerfectNumbers.Core/MersenneDivisorCycles.cs
@@ -411,7 +411,7 @@ public class MersenneDivisorCycles
 		// Atomic.Add(ref _tryFactorIntoCountsInternalHits, 1UL);
 		// Console.WriteLine($"MersenneDivisorCycles.TryFactorIntoCountsInternal hits {Volatile.Read(ref _tryFactorIntoCountsInternalHits)}");
 
-		if (PrimeTester.IsPrimeGpu(remaining))
+		if (PrimeTester.IsPrimeCpu(remaining, CancellationToken.None))
 		// if (PrimeTester.IsPrimeCpu(remaining, CancellationToken.None))
 		{
 			AddFactor(counts, remaining);
@@ -937,7 +937,7 @@ public class MersenneDivisorCycles
 		// }
 
         // if (!skipPrimeOrderHeuristic && HeuristicPrimeTester.Exclusive.IsPrimeCpu(divisor, CancellationToken.None))
-        if (!skipPrimeOrderHeuristic && PrimeTester.IsPrimeGpu(divisor))
+        if (!skipPrimeOrderHeuristic && PrimeTester.IsPrimeCpu(divisor, CancellationToken.None))
         // if (!skipPrimeOrderHeuristic && PrimeTester.IsPrimeCpu(divisor, CancellationToken.None))
         {
             ulong computedOrder = PrimeOrderCalculator.Calculate(