diff -Nru NetHack-3.6.7.orig/sys/unix/Makefile.utl NetHack-3.6.7/sys/unix/Makefile.utl
--- NetHack-3.6.7.orig/sys/unix/Makefile.utl	2023-02-15 22:52:57.000000000 +0100
+++ NetHack-3.6.7/sys/unix/Makefile.utl	2023-10-08 15:12:17.968093996 +0200
@@ -94,8 +94,8 @@
 # flags for debugging:
 # CFLAGS = -g -I../include
 
-#CFLAGS = -O -I../include
-#LFLAGS =
+CFLAGS = -O -I../include
+LFLAGS =
 
 # we specify C preprocessor flags via CFLAGS; files built with default rules
 # might include $(CPPFLAGS) which could get a value from user's environment;
@@ -111,11 +111,11 @@
 
 # yacc/lex programs to use to generate *_comp.h, *_lex.c, and *_yacc.c.
 # if, instead of yacc/lex you have bison/flex, comment/uncomment the following.
-YACC     = yacc
-LEX      = lex
-# YACC     = bison -y
+# YACC     = yacc
+# LEX      = lex
+YACC     = bison -y
 # YACC     = byacc
-# LEX      = flex
+LEX      = flex
 
 # these are the names of the output files from YACC/LEX. Under MS-DOS
 # and similar systems, they may differ