diff --git a/CMakeLists.txt b/CMakeLists.txt
index 9487ab9..eb030e2 100644
--- a/CMakeLists.txt
+++ b/CMakeLists.txt
@@ -72,9 +72,9 @@ SET_TARGET_PROPERTIES(loudgain PROPERTIES
   COMPILE_FLAGS "-Wall -pedantic -g"
 )
 
-SET(CMAKE_C_FLAGS "-std=gnu99 -D_GNU_SOURCE")
+SET(CMAKE_C_FLAGS "${CMAKE_C_FLAGS} -std=gnu99 -D_GNU_SOURCE")
 
-SET(CMAKE_CXX_FLAGS "-std=gnu++11 -D_GNU_SOURCE")
+SET(CMAKE_CXX_FLAGS "${CMAKE_CXX_FLAGS} -std=gnu++11 -D_GNU_SOURCE")
 
 INSTALL(TARGETS loudgain DESTINATION ${CMAKE_INSTALL_PREFIX}/bin)