diff --git a/Source/CTest/cmCTestRunTest.cxx b/Source/CTest/cmCTestRunTest.cxx
index 9e3c9fcf0..ff55528b4 100644
--- a/Source/CTest/cmCTestRunTest.cxx
+++ b/Source/CTest/cmCTestRunTest.cxx
@@ -116,10 +116,10 @@ void cmCTestRunTest::CompressOutput()
   unsigned char *encoded_buffer
     = new unsigned char[static_cast<int>(outSize * 1.5)];
 
-  unsigned long rlen
+  size_t rlen
     = cmsysBase64_Encode(out, strm.total_out, encoded_buffer, 1);
 
-  for(unsigned long i = 0; i < rlen; i++)
+  for(size_t i = 0; i < rlen; i++)
     {
     this->CompressedOutput += encoded_buffer[i];
     }
diff --git a/Source/CTest/cmCTestTestHandler.cxx b/Source/CTest/cmCTestTestHandler.cxx
index f330e584b..8518a90d4 100644
--- a/Source/CTest/cmCTestTestHandler.cxx
+++ b/Source/CTest/cmCTestTestHandler.cxx
@@ -1976,9 +1976,8 @@ std::string cmCTestTestHandler::GenerateRegressionImages(
             = new unsigned char [ static_cast<int>(
                 static_cast<double>(len) * 1.5 + 5.0) ];
 
-          unsigned long rlen
+          size_t rlen
             = cmsysBase64_Encode(file_buffer, len, encoded_buffer, 1);
-          unsigned long cc;
 
           ostr
             << "\t\t\t<NamedMeasurement"
@@ -1988,7 +1987,7 @@ std::string cmCTestTestHandler::GenerateRegressionImages(
             << measurementfile.match(4) << "\""
             << " encoding=\"base64\""
             << ">" << std::endl << "\t\t\t\t<Value>";
-          for ( cc = 0; cc < rlen; cc ++ )
+          for (size_t cc = 0; cc < rlen; cc ++ )
             {
             ostr << encoded_buffer[cc];
             if ( cc % 60 == 0 && cc )
diff --git a/Source/cmCTest.cxx b/Source/cmCTest.cxx
index 814c4e02f..1362a503c 100644
--- a/Source/cmCTest.cxx
+++ b/Source/cmCTest.cxx
@@ -1701,11 +1701,11 @@ std::string cmCTest::Base64EncodeFile(std::string file)
   unsigned char *encoded_buffer
     = new unsigned char [ (len * 3) / 2 + 5 ];
 
-  unsigned long rlen
+  size_t const rlen
     = cmsysBase64_Encode(file_buffer, len, encoded_buffer, 1);
 
   std::string base64 = "";
-  for(unsigned long i = 0; i < rlen; i++)
+  for(size_t i = 0; i < rlen; i++)
     {
     base64 += encoded_buffer[i];
     }
@@ -3193,7 +3193,7 @@ bool cmCTest::CompressString(std::string& str)
   unsigned char* base64EncodedBuffer
     = new unsigned char[(outSize * 3) / 2];
 
-  unsigned long rlen
+  size_t rlen
     = cmsysBase64_Encode(out, strm.total_out, base64EncodedBuffer, 1);
 
   str = "";