fix gcc warnings
diff --git a/CMakeLists.txt b/CMakeLists.txt
index a8558a3..96219e2 100644
--- a/CMakeLists.txt
+++ b/CMakeLists.txt
@@ -85,10 +85,10 @@
 
 if (CMAKE_CXX_COMPILER_ID MATCHES "Clang")
   # using regular Clang or AppleClang
-  set(CMAKE_CXX_FLAGS "${CMAKE_CXX_FLAGS} -Wall -std=c++11")
+  set(CMAKE_CXX_FLAGS "${CMAKE_CXX_FLAGS} -std=c++11 -Wall")
 elseif ("${CMAKE_CXX_COMPILER_ID}" STREQUAL "GNU")
   # using GCC
-  set(CMAKE_CXX_FLAGS "${CMAKE_CXX_FLAGS} -Wall -std=c++0x")
+  set(CMAKE_CXX_FLAGS "${CMAKE_CXX_FLAGS} -std=c++0x -Wall -Wextra -Wpedantic")
 endif()
 
 IF(JSONCPP_WITH_WARNING_AS_ERROR)