diff --git a/source/ur/ur.hpp b/source/ur/ur.hpp
index cf84bb437d..f60e7eff70 100644
--- a/source/ur/ur.hpp
+++ b/source/ur/ur.hpp
@@ -352,20 +352,29 @@ static inline void roundToHighestFactorOfGlobalSizeIn3d(
     size_t *ThreadsPerBlock, const size_t *GlobalSize,
     const size_t *MaxBlockDim, const size_t MaxBlockSize,
     const size_t WorkDim) {
-  ThreadsPerBlock[0] = std::min(GlobalSize[0], MaxBlockDim[0]);
-  // Make the X dim a factor of 2
+
+  auto findLowerFactor = [](size_t &ThreadsPerBlock) {
+    return !isPowerOf2(ThreadsPerBlock) && ThreadsPerBlock > 32 &&
+           --ThreadsPerBlock;
+  };
+  assert(GlobalSize[0] && "GlobalSize[0] cannot be zero");
+  assert(GlobalSize[1] && "GlobalSize[1] cannot be zero");
+  assert(GlobalSize[2] && "GlobalSize[2] cannot be zero");
+
+  ThreadsPerBlock[0] =
+      std::min(GlobalSize[0], std::min(MaxBlockSize, MaxBlockDim[0]));
   do {
     roundToHighestFactorOfGlobalSize(ThreadsPerBlock[0], GlobalSize[0]);
-  } while (WorkDim == 3 && !isPowerOf2(ThreadsPerBlock[0]) &&
-           ThreadsPerBlock[0] > 32 && --ThreadsPerBlock[0]);
+  } while (WorkDim == 3 && findLowerFactor(ThreadsPerBlock[0]));
+  assert(ThreadsPerBlock[0] && "ThreadsPerBlock[0] cannot be zero");
 
   ThreadsPerBlock[1] =
       std::min(GlobalSize[1],
                std::min(MaxBlockSize / ThreadsPerBlock[0], MaxBlockDim[1]));
   do {
     roundToHighestFactorOfGlobalSize(ThreadsPerBlock[1], GlobalSize[1]);
-  } while (WorkDim == 2 && !isPowerOf2(ThreadsPerBlock[1]) &&
-           ThreadsPerBlock[1] > 32 && --ThreadsPerBlock[1]);
+  } while (WorkDim == 2 && findLowerFactor(ThreadsPerBlock[1]));
+  assert(ThreadsPerBlock[1] && "ThreadsPerBlock[1] cannot be zero");
 
   ThreadsPerBlock[2] = std::min(
       GlobalSize[2],
@@ -373,6 +382,6 @@ static inline void roundToHighestFactorOfGlobalSizeIn3d(
                MaxBlockDim[2]));
   do {
     roundToHighestFactorOfGlobalSize(ThreadsPerBlock[2], GlobalSize[2]);
-  } while (WorkDim == 1 && !isPowerOf2(ThreadsPerBlock[2]) &&
-           ThreadsPerBlock[2] > 32 && --ThreadsPerBlock[2]);
+  } while (WorkDim == 1 && findLowerFactor(ThreadsPerBlock[2]));
+  assert(ThreadsPerBlock[2] && "ThreadsPerBlock[2] cannot be zero");
 }