diff --git a/CMakeLists.txt b/CMakeLists.txt
index babea3ee9448486ff768e1b8146e060c2481feb5..6f762ad8e9ea9178678be2a325844debd08c8832 100644
--- a/CMakeLists.txt
+++ b/CMakeLists.txt
@@ -118,11 +118,11 @@ add_definitions(-DIN_LINPHONE)
 
 
 if(MSVC)
-	set(CMAKE_C_FLAGS "/W3")
-	set(CMAKE_CXX_FLAGS "/W3")
+	set(CMAKE_C_FLAGS "${CMAKE_C_FLAGS} /W3")
+	set(CMAKE_CXX_FLAGS "${CMAKE_CXX_FLAGS} /W3")
 else()
-	set(CMAKE_C_FLAGS "-Wall -Wuninitialized -Wdeclaration-after-statement -fno-strict-aliasing -Werror")
-	set(CMAKE_CXX_FLAGS "-Wall -Wuninitialized -Werror")
+	set(CMAKE_C_FLAGS "${CMAKE_C_FLAGS} -Wall -Wuninitialized -Wdeclaration-after-statement -fno-strict-aliasing -Werror")
+	set(CMAKE_CXX_FLAGS "${CMAKE_CXX_FLAGS} -Wall -Wuninitialized -Werror")
 	if(CMAKE_C_COMPILER_ID STREQUAL "Clang")
 		set(CMAKE_C_FLAGS "${CMAKE_C_FLAGS} -Qunused-arguments -Wno-array-bounds")
 	endif()