https://bugs.gentoo.org/907988
--- a/configure.in	2016-10-01 23:46:01.000000000 +0200
+++ b/configure.in	2023-06-10 22:44:20.873592074 +0200
@@ -82,11 +82,14 @@
 AC_CANONICAL_SYSTEM
 
 dnl Check for programs.
-AC_PROG_YACC
 AC_PROG_LEX
 AC_PROG_CC
 AC_PROG_INSTALL
 
+AC_ARG_VAR([BISON], [bison command for yacc parsing])
+AC_CHECK_PROG([BISON], [bison -y], [bison -y], [no])
+AS_IF([test "x$BISON" = "xno"], [AC_MSG_ERROR([bison not found])])
+
 dnl Checks for typedefs, structures, and compiler characteristics.
 AC_C_CONST
 AC_C_INLINE
--- a/Makefile.in	2016-10-01 23:46:00.000000000 +0200
+++ b/Makefile.in	2023-06-10 23:00:25.278904190 +0200
@@ -21,8 +21,8 @@
 CFLAGS = @CFLAGS@ @CPPFLAGS@
 LDFLAGS = @LDFLAGS@ @LIBS@
 
-YACC = @YACC@
-YACCFLAGS = -d
+BISON = @BISON@
+BISONFLAGS = -d
 
 LEX = @LEX@
 LEXFLAGS = -t 
@@ -62,7 +62,7 @@
 	$(CC) $(CFLAGS) -o vtund $(OBJS) $(LFD_OBJS) $(LDFLAGS)
 
 cfg_file.tab.h:
-	$(YACC) $(YACCFLAGS) -b cfg_file cfg_file.y
+	$(BISON) $(BISONFLAGS) -b cfg_file cfg_file.y
 
 cfg_file.tab.c: cfg_file.y cfg_kwords.h config.h cfg_file.tab.h