diff --git a/CMakeLists.txt b/CMakeLists.txt
index ba32022..90eb14e 100644
--- a/CMakeLists.txt
+++ b/CMakeLists.txt
@@ -97,7 +97,7 @@ endif( MSVC )
 
 if (CMAKE_CXX_COMPILER_ID MATCHES "Clang")
   # using regular Clang or AppleClang
-  set(CMAKE_CXX_FLAGS "${CMAKE_CXX_FLAGS} -std=c++11 -Wall")
+  set(CMAKE_CXX_FLAGS "${CMAKE_CXX_FLAGS} -std=c++11 -Wall -Wshorten-64-to-32")
 elseif ("${CMAKE_CXX_COMPILER_ID}" STREQUAL "GNU")
   # using GCC
   set(CMAKE_CXX_FLAGS "${CMAKE_CXX_FLAGS} -std=c++0x -Wall -Wextra -pedantic")