diff --git a/configure.ac b/configure.ac
index 1733a631a..7fd9538c2 100644
--- a/configure.ac
+++ b/configure.ac
@@ -23,7 +23,7 @@ AC_PROG_CC
 AC_PROG_CC_C99
 AM_PROG_CC_C_O
 AC_PROG_CXX
-AX_CXX_COMPILE_STDCXX(11,, optional)
+AX_CXX_COMPILE_STDCXX(11)
 AC_SYS_LARGEFILE
 PKG_PROG_PKG_CONFIG([0.20])
 AM_MISSING_PROG([RAGEL], [ragel])