diff --git a/Release/src/CMakeLists.txt b/Release/src/CMakeLists.txt
index e15aeb7fc..128f6d6af 100644
--- a/Release/src/CMakeLists.txt
+++ b/Release/src/CMakeLists.txt
@@ -185,12 +185,12 @@ endif()
 
 configure_pch(cpprest stdafx.h pch/stdafx.cpp /Zm120)
 
-if(CMAKE_CXX_COMPILER_ID MATCHES "Clang" OR CMAKE_CXX_COMPILER_ID MATCHES "GNU")
+if(CMAKE_CXX_COMPILER_ID MATCHES "Clang" OR CMAKE_CXX_COMPILER_ID MATCHES "GNU" AND NOT MSVC)
   if(WERROR)
     target_compile_options(cpprest PRIVATE -Werror)
   endif()
   target_compile_options(cpprest PRIVATE -pedantic ${WARNINGS})
-elseif(CMAKE_CXX_COMPILER_ID MATCHES "MSVC")
+elseif(CMAKE_CXX_COMPILER_ID MATCHES "MSVC" OR CMAKE_CXX_COMPILER_FRONTEND_VARIANT MATCHES "MSVC")
   if(WERROR)
     target_compile_options(cpprest PRIVATE /WX ${WARNINGS})
   endif()
diff --git a/Release/src/streams/fileio_win32.cpp b/Release/src/streams/fileio_win32.cpp
index 057dd9b67..a65439cb7 100644
--- a/Release/src/streams/fileio_win32.cpp
+++ b/Release/src/streams/fileio_win32.cpp
@@ -616,7 +616,7 @@ size_t _fill_buffer_fsb(_In_ _file_info_impl* fInfo,
                 // pending
                 return read;
 
-            case (-1):
+            case ((size_t)(-1)):
                 // error
                 delete cb;
                 return read;
@@ -668,7 +668,7 @@ size_t _fill_buffer_fsb(_In_ _file_info_impl* fInfo,
                 // pending
                 return read;
 
-            case (-1):
+            case ((size_t)(-1)):
                 // error
                 delete cb;
                 return read;
@@ -719,7 +719,7 @@ size_t _fill_buffer_fsb(_In_ _file_info_impl* fInfo,
                 // pending
                 return read;
 
-            case (-1):
+            case ((size_t)(-1)):
                 // error
                 delete cb;
                 return read;