diff --git a/source/world_builder/utilities.cc b/source/world_builder/utilities.cc
index 6e2e7fd4f..85eb25c1f 100644
--- a/source/world_builder/utilities.cc
+++ b/source/world_builder/utilities.cc
@@ -1183,7 +1183,7 @@ namespace WorldBuilder
           MPI_Comm_rank(comm, &my_rank);
           if (my_rank == 0)
             {
-              uint64_t filesize;
+              int filesize;
               std::ifstream filestream;
               filestream.open(filename.c_str());
               WBAssertThrow (filestream.is_open(), std::string("Could not open file <") + filename + ">.");
@@ -1217,9 +1217,9 @@ namespace WorldBuilder
                 }
 
               data_string = datastream.str();
-              filesize = data_string.size();
-              WBAssertThrow(filesize < std::numeric_limits<uint64_t>::max(),
+              WBAssertThrow(data_string.size() < std::numeric_limits<int>::max(),
                             "File to large to be send with MPI.");
+              filesize = static_cast<int>(data_string.size());
 
               // Distribute data_size and data across processes
               int ierr = MPI_Bcast(&filesize, 1, MPI_UNSIGNED, 0, comm);
@@ -1227,7 +1227,7 @@ namespace WorldBuilder
 
               // Receive and store data
               ierr = MPI_Bcast(&data_string[0],
-                               static_cast<int>(filesize),
+                               filesize,
                                MPI_CHAR,
                                0,
                                comm);
@@ -1510,12 +1510,12 @@ namespace WorldBuilder
     multiply_3x3_matrices(const std::array<std::array<double,3>,3> mat1, const std::array<std::array<double,3>,3> mat2)
     {
       std::array<std::array<double,3>,3> result;
-      for (int i = 0; i < 3; i++)
+      for (size_t i = 0; i < 3; i++)
         {
-          for (int j = 0; j < 3; j++)
+          for (size_t j = 0; j < 3; j++)
             {
               result[i][j] = 0;
-              for (int k = 0; k < 3; k++)
+              for (size_t k = 0; k < 3; k++)
                 {
                   result[i][j] += mat1[i][k] * mat2[k][j];
                 }
diff --git a/tests/unit_tests/utilities.cc b/tests/unit_tests/utilities.cc
index a2ef6a924..670cb86bf 100644
--- a/tests/unit_tests/utilities.cc
+++ b/tests/unit_tests/utilities.cc
@@ -40,54 +40,54 @@ TEST_CASE("multiply 3x3 matrices")
   std::array<std::array<double,3>,3> result6 = {{{{39.9,36.8,33.7}},{{60,47.5,35}},{{-94.2,-80.5,-66.8}}}}; //mat3*mat2
 
   std::array<std::array<double,3>,3> result7 = Utilities::multiply_3x3_matrices(mat1, mat2);
-  for (int i = 0; i < 3; i++)
+  for (size_t i = 0; i < 3; i++)
     {
-      for (int j = 0; j < 3; j++)
+      for (size_t j = 0; j < 3; j++)
         {
           CHECK(result1[i][j] == Approx(result7[i][j]));
         }
     }
 
   std::array<std::array<double,3>,3> result8 = Utilities::multiply_3x3_matrices(mat2, mat1);
-  for (int i = 0; i < 3; i++)
+  for (size_t i = 0; i < 3; i++)
     {
-      for (int j = 0; j < 3; j++)
+      for (size_t j = 0; j < 3; j++)
         {
           CHECK(result2[i][j] == Approx(result8[i][j]));
         }
     }
 
   std::array<std::array<double,3>,3> result9 = Utilities::multiply_3x3_matrices(mat1, mat3);
-  for (int i = 0; i < 3; i++)
+  for (size_t i = 0; i < 3; i++)
     {
-      for (int j = 0; j < 3; j++)
+      for (size_t j = 0; j < 3; j++)
         {
           CHECK(result3[i][j] == Approx(result9[i][j]));
         }
     }
 
   std::array<std::array<double,3>,3> result10 = Utilities::multiply_3x3_matrices(mat3, mat1);
-  for (int i = 0; i < 3; i++)
+  for (size_t i = 0; i < 3; i++)
     {
-      for (int j = 0; j < 3; j++)
+      for (size_t j = 0; j < 3; j++)
         {
           CHECK(result4[i][j] == Approx(result10[i][j]));
         }
     }
 
   std::array<std::array<double,3>,3> result11 = Utilities::multiply_3x3_matrices(mat2, mat3);
-  for (int i = 0; i < 3; i++)
+  for (size_t i = 0; i < 3; i++)
     {
-      for (int j = 0; j < 3; j++)
+      for (size_t j = 0; j < 3; j++)
         {
           CHECK(result5[i][j] == Approx(result11[i][j]));
         }
     }
 
   std::array<std::array<double,3>,3> result12 = Utilities::multiply_3x3_matrices(mat3, mat2);
-  for (int i = 0; i < 3; i++)
+  for (size_t i = 0; i < 3; i++)
     {
-      for (int j = 0; j < 3; j++)
+      for (size_t j = 0; j < 3; j++)
         {
           CHECK(result6[i][j] == Approx(result12[i][j]));
         }