diff --git a/m4/slibtool.m4 b/m4/slibtool.m4
index 25c37a3..bf1c4e1 100644
--- a/m4/slibtool.m4
+++ b/m4/slibtool.m4
@@ -402,8 +402,11 @@ if [[ -z "${LEX}" ]]; then
 	AC_CHECK_PROG([LEX],[lex],[lex])
 fi
 
+slibtool_lex_output_root="${ac_cv_prog_lex_root:-lex.yy}"
+
 AC_SUBST([LEX])
 AC_SUBST([LEXLIB])
+AC_SUBST([LEX_OUTPUT_ROOT],["${slibtool_lex_output_root}"])
 ])