diff -ur ../tmp/m4/ntl-check.m4 m4/ntl-check.m4
--- ../tmp/m4/ntl-check.m4	2016-12-29 09:44:18.000000000 -0500
+++ m4/ntl-check.m4	2017-06-07 10:23:21.494542047 -0400
@@ -58,7 +58,7 @@
 		NTL_LIBS="-lntl"
 	fi
 ###	CFLAGS="${BACKUP_CFLAGS} ${NTL_CFLAGS} ${GMP_CFLAGS}"
-	CXXFLAGS="${BACKUP_CFLAGS} ${BACKUP_CXXFLAGS} ${NTL_CFLAGS} ${GMP_CFLAGS}"
+	CXXFLAGS="${BACKUP_CXXFLAGS} ${NTL_CFLAGS} ${GMP_CFLAGS}"
 	LIBS="${BACKUP_LIBS} ${NTL_LIBS} ${GMP_LIBS}"
 
 	AC_TRY_LINK(
