diff --git a/vtkm/filter/testing/UnitTestMultiBlockCellFilter.cxx b/vtkm/filter/testing/UnitTestMultiBlockCellFilter.cxx
index 3d4aab050..ba7a07d1d 100644
--- a/vtkm/filter/testing/UnitTestMultiBlockCellFilter.cxx
+++ b/vtkm/filter/testing/UnitTestMultiBlockCellFilter.cxx
@@ -74,7 +74,7 @@ vtkm::cont::MultiBlock UniformMultiBlockBuilder(std::size_t BlockNum)
   vtkm::Vec<T,2> origin(0);
   vtkm::Vec<T,2> spacing(1);
   vtkm::cont::MultiBlock Blocks;
-  for (std::size_t BlockId = 0; BlockId < BlockNum; BlockId++)
+  for (std::size_t BlockId = 0; BlockId < static_cast<vtkm::Id>(BlockNum); BlockId++)
   {
     vtkm::Id2 dimensions( (BlockId+2) * (BlockId+2), (BlockId+2) * (BlockId+2) );
     vtkm::Id numPoints = dimensions[0] * dimensions[1];
diff --git a/vtkm/filter/testing/UnitTestMultiBlockFieldFilter.cxx b/vtkm/filter/testing/UnitTestMultiBlockFieldFilter.cxx
index 6f4e615fe..c5fc0bc98 100644
--- a/vtkm/filter/testing/UnitTestMultiBlockFieldFilter.cxx
+++ b/vtkm/filter/testing/UnitTestMultiBlockFieldFilter.cxx
@@ -61,7 +61,7 @@ vtkm::cont::MultiBlock MultiBlockBuilder(std::size_t BlockNum)
   vtkm::Vec<T,2> origin(0);
   vtkm::Vec<T,2> spacing(1);
   vtkm::cont::MultiBlock Blocks;
-  for (std::size_t BlockId = 0; BlockId < BlockNum; BlockId++)
+  for (vtkm::Id BlockId = 0; BlockId < static_cast<vtkm::Id>(BlockNum); BlockId++)
   {
     vtkm::Id2 dimensions( (BlockId+2) * (BlockId+2), (BlockId+2) * (BlockId+2) );
     vtkm::Id numCells = (dimensions[0]-1) * (dimensions[1]-1);