diff --git a/configure.ac b/configure.ac
index 7e673b51..956ce4cd 100644
--- a/configure.ac
+++ b/configure.ac
@@ -262,7 +262,8 @@ if ! "$LEX_IS_FLEX" || test "X$LEX" = X:; then
   LEX=:
 fi
 AM_CONDITIONAL([FLEX_WORKS], [$LEX_IS_FLEX && $FLEX_SUPPORTS_HEADER_OPT])
-AM_CONDITIONAL([FLEX_CXX_WORKS], [$LEX_WORKS && test $bison_cv_cxx_works = yes])
+AM_CONDITIONAL([FLEX_CXX_WORKS],
+  [$LEX_IS_FLEX && $FLEX_SUPPORTS_HEADER_OPT && test $bison_cv_cxx_works = yes])
 AC_PROG_YACC
 AC_PROG_RANLIB
 AC_PROG_GNU_M4