diff --git a/CMakeLists.txt b/CMakeLists.txt
index 4296b235..b4a36bd9 100644
--- a/CMakeLists.txt
+++ b/CMakeLists.txt
@@ -38,6 +38,7 @@ add_cxx_compiler_flag(-Wextra)
 add_cxx_compiler_flag(-Wshadow)
 add_cxx_compiler_flag(-Werror)
 add_cxx_compiler_flag(-pedantic-errors)
+add_cxx_compiler_flag(-Wshorten-64-to-32)
 # TODO(ericwf): enable this for g++
 #add_cxx_compiler_flag(-Wzero-as-null-pointer-constant)
 # Release flags