diff --git a/CMakeLists.txt b/CMakeLists.txt
index 418afae..02c56b5 100644
--- a/CMakeLists.txt
+++ b/CMakeLists.txt
@@ -23,11 +23,18 @@ include(GNUInstallDirs)
 include(CheckCXXSourceCompiles)
 include(CheckCXXCompilerFlag)
 
-if(CMAKE_GENERATOR STREQUAL "Ninja")
-  if("${CMAKE_CXX_COMPILER_ID}" STREQUAL "GNU")
-    add_compile_options(-fdiagnostics-color=always)
-  elseif("${CMAKE_CXX_COMPILER_ID}" STREQUAL "Clang")
-    add_compile_options(-fcolor-diagnostics)
+if(PROJECT_IS_TOP_LEVEL)
+  if(CMAKE_GENERATOR STREQUAL "Ninja")
+    if("${CMAKE_CXX_COMPILER_ID}" STREQUAL "GNU")
+      SET(CMAKE_CXX_FLAGS "${CMAKE_CXX_FLAGS} -fdiagnostics-color=always")
+    elseif("${CMAKE_CXX_COMPILER_ID}" STREQUAL "Clang")
+      SET(CMAKE_CXX_FLAGS "${CMAKE_CXX_FLAGS} -fcolor-diagnostics")
+    endif()
+    if("${CMAKE_C_COMPILER_ID}" STREQUAL "GNU")
+      SET(CMAKE_C_FLAGS "${CMAKE_C_FLAGS} -fdiagnostics-color=always")
+    elseif("${CMAKE_C_COMPILER_ID}" STREQUAL "Clang")
+      SET(CMAKE_C_FLAGS "${CMAKE_C_FLAGS} -fcolor-diagnostics")
+    endif()
   endif()
 endif()