diff --git a/CMakeLists.txt b/CMakeLists.txt
index 08ef64f..95e070f 100644
--- a/CMakeLists.txt
+++ b/CMakeLists.txt
@@ -47,7 +47,7 @@ if(CXXOPTS_USE_UNICODE_HELP)
   pkg_check_modules(ICU REQUIRED icu-uc)
 
   set(CXXOPTS_LINKER_LIBRARIES "${ICU_LIBRARIES}")
-  set(CMAKE_CXX_FLAGS "${CMAKE_CXX_FLAGS} -DCXXOPTS_USE_UNICODE")
+  set(CMAKE_CXX_FLAGS "${CMAKE_CXX_FLAGS} ${ICU_CFLAGS} -DCXXOPTS_USE_UNICODE")
 
 endif()