diff --git a/configure.ac b/configure.ac
index a6208ef5..49556a3c 100644
--- a/configure.ac
+++ b/configure.ac
@@ -11,7 +11,7 @@ if test -z $CXXFLAGS; then
 	CXXFLAGS="-fpic -Wall -Wno-unused-function -Wextra -g -O2"
 fi
 AC_PROG_CXX([g++-6 g++-5 g++-4.9 g++-4.8 g++])
-AX_CXX_COMPILE_STDCXX([11], [noext], [mandatory])
+AX_CXX_COMPILE_STDCXX([11], [ext], [mandatory])
 
 AC_CHECK_HEADERS([arpa/inet.h \
 		  dirent.h \