diff --git a/Source/CTest/cmCTestCurl.cxx b/Source/CTest/cmCTestCurl.cxx
index 3ad474980c..69c57938fe 100644
--- a/Source/CTest/cmCTestCurl.cxx
+++ b/Source/CTest/cmCTestCurl.cxx
@@ -55,7 +55,7 @@ size_t curlDebugCallback(CURL* /*unused*/, curl_infotype /*unused*/,
                          char* chPtr, size_t size, void* data)
 {
   cm::append(*static_cast<std::vector<char>*>(data), chPtr, chPtr + size);
-  return size;
+  return 0;
 }
 }
 
diff --git a/Source/CTest/cmCTestSubmitHandler.cxx b/Source/CTest/cmCTestSubmitHandler.cxx
index a8f201a8a8..22ab48f57e 100644
--- a/Source/CTest/cmCTestSubmitHandler.cxx
+++ b/Source/CTest/cmCTestSubmitHandler.cxx
@@ -110,7 +110,7 @@ static size_t cmCTestSubmitHandlerCurlDebugCallback(CURL* /*unused*/,
 {
   cm::append(*static_cast<cmCTestSubmitHandlerVectorOfChar*>(data), chPtr,
              chPtr + size);
-  return size;
+  return 0;
 }
 
 cmCTestSubmitHandler::cmCTestSubmitHandler()