diff --git a/CMakeLists.txt b/CMakeLists.txt
index 1583daa..97e4de0 100644
--- a/CMakeLists.txt
+++ b/CMakeLists.txt
@@ -103,7 +103,7 @@ endif()
 
 if (CMAKE_CXX_COMPILER_ID MATCHES "Clang")
   # using regular Clang or AppleClang
-  set(CMAKE_CXX_FLAGS "${CMAKE_CXX_FLAGS} -std=c++11 -Wall -Wconversion -Wshadow -Wno-sign-conversion -Werror=conversion")
+  set(CMAKE_CXX_FLAGS "${CMAKE_CXX_FLAGS} -std=c++11 -Wall -Wconversion -Wshadow -Wno-sign-conversion -Werror=conversion -Werror=sign-compare")
 elseif (CMAKE_CXX_COMPILER_ID STREQUAL "GNU")
   # using GCC
   set(CMAKE_CXX_FLAGS "${CMAKE_CXX_FLAGS} -std=c++11 -Wall -Wconversion -Wshadow -Wextra -Werror=conversion")