Appveyor MinGW build
diff --git a/cmake/tests.cmake b/cmake/tests.cmake
index ec790e3..f91567b 100644
--- a/cmake/tests.cmake
+++ b/cmake/tests.cmake
@@ -204,6 +204,10 @@
   add_compile_options(-DGOOGLE_PROTOBUF_TEST_PLUGIN_PATH="$<TARGET_FILE:test_plugin>")
 endif()
 
+if(MINGW)
+  set_source_files_properties(${tests_files} PROPERTIES COMPILE_FLAGS "-Wno-narrowing")
+endif()
+
 add_executable(tests ${tests_files} ${common_test_files} ${tests_proto_files} ${lite_test_proto_files})
 target_link_libraries(tests libprotoc libprotobuf gmock_main)