diff --git a/configure.in b/configure.in
index 737c41e4..bf92e683 100644
--- a/configure.in
+++ b/configure.in
@@ -60,6 +60,7 @@ AC_SUBST(vpath_build)
 AC_CHECK_PROG(HAVE_GNUSED,gnused,yes,no)
 AC_CHECK_PROG(HAVE_GSED,gsed,yes,no)
 AC_CHECK_PROG(HAVE_SED,sed,yes,no)
+AC_CHECK_PROG(HAVE_FLEX,flex,yes,no)
 
 if test "$HAVE_GNUSED" = yes; then
  SED=gnused
@@ -72,6 +73,7 @@ else
 fi
 AC_SUBST(SED)
 
+AS_IF([test x"$HAVE_FLEX" != x"yes"], AC_MSG_ERROR([flex should be installed first]))
 
 AC_CONFIG_FILES([Makefile])
 AC_CONFIG_FILES([Makefile.global])