diff --git a/cmake/FairMQProjectSettings.cmake b/cmake/FairMQProjectSettings.cmake
index df1eca68..a3f5158a 100644
--- a/cmake/FairMQProjectSettings.cmake
+++ b/cmake/FairMQProjectSettings.cmake
@@ -85,7 +85,7 @@ if(CMAKE_GENERATOR STREQUAL "Ninja" AND
     (CMAKE_CXX_COMPILER_ID STREQUAL "Clang" AND NOT CMAKE_CXX_COMPILER_VERSION VERSION_LESS 3.5)))
   # Force colored warnings in Ninja's output, if the compiler has -fdiagnostics-color support.
   # Rationale in https://github.com/ninja-build/ninja/issues/814
-  list(APPEND CMAKE_CXX_FLAGS "-fdiagnostics-color=always")
+  set(CMAKE_CXX_FLAGS "${CMAKE_CXX_FLAGS} -fdiagnostics-color=always")
 endif()
 
 if(NOT DEFINED PROJECT_VERSION_TWEAK)