diff --git a/sample/Makefile b/sample/Makefile
index 9166360..a10144f 100644
--- a/sample/Makefile
+++ b/sample/Makefile
@@ -1,7 +1,7 @@
 XBYAK_INC=../xbyak/xbyak.h
 CXX?=g++
 
-BOOST_EXIST=$(shell echo "#include <boost/spirit/core.hpp>" | $(CXX) -x c++ -c - 2>/dev/null && echo 1)
+BOOST_EXIST=$(shell echo "#include <boost/spirit/core.hpp>" | $CXX -x c++ -c - 2>/dev/null && echo 1)
 UNAME_M=$(shell uname -m)
 
 ONLY_64BIT=0