Index: configure
===================================================================
--- configure	(revision 6e7e2b36dcaa528c1778f81efe7654e171fb2197)
+++ configure	(revision c3a438560523e77e6d19c2dc3cc32605a6c1e41a)
@@ -4528,4 +4528,5 @@
 
 	# deprecated
+# These are often not installed and people miss seeing the "no", so stop the configure.
 for ac_prog in 'bison -y' byacc
 do
@@ -4571,4 +4572,5 @@
 test -n "$YACC" || YACC="yacc"
 
+if test "${YACC}" = "yacc" ; then echo "Error: bison required." ; exit 1 ; fi
 
 for ac_prog in flex lex
@@ -4730,4 +4732,5 @@
 
 fi
+if test "${LEX}" = "lex" ; then echo "Error: flex required." ; exit 1 ; fi
 
 { $as_echo "$as_me:${as_lineno-$LINENO}: checking whether ${MAKE-make} sets \$(MAKE)" >&5