diff --git a/CMakeLists.txt b/CMakeLists.txt
index 1e3098c..4d17af8 100644
--- a/CMakeLists.txt
+++ b/CMakeLists.txt
@@ -135,7 +135,7 @@
         set(CMAKE_C_FLAGS "${CMAKE_C_FLAGS} -Wlogical-op")
     endif()
     if (GCC_VERSION VERSION_GREATER 4.8 OR GCC_VERSION VERSION_EQUAL 4.8)
-        set(CMAKE_C_FLAGS "${CMAKE_C_FLAGS} -Wshadow")
+        set(CMAKE_C_FLAGS "${CMAKE_C_FLAGS} -Wshadow -Wformat-signedness")
     endif()
     set(CMAKE_C_FLAGS_RELEASE     "-O2")
     set(CMAKE_C_FLAGS_DEBUG       "-O0 -g3")