diff --git a/ldefs.h b/ldefs.h
index 408fe15..6987c31 100644
--- a/ldefs.h
+++ b/ldefs.h
@@ -155,6 +155,7 @@ extern lchar yycgidtbl[];
 extern int yycgid(wchar_t);
 extern Boolean handleeuc; /* TRUE iff -w or -e option is specified. */
 extern Boolean widecio; /* TRUE iff -w option is specified. */
+extern Boolean caseless; /* TRUE iff -i option is specified. */
 
 #define	DEFSECTION 1
 #define	RULESECTION 2
diff --git a/lex.1 b/lex.1
index 5e041c5..23d6857 100644
--- a/lex.1
+++ b/lex.1
@@ -89,6 +89,10 @@ Generates output that can handle multibyte characters,
 with \fIyytext[]\fR being of type \fIunsigned char[]\fR.
 This option is an extension.
 .TP
+.B \-i
+Generates a case insensitive scanner (%option case-insensitive)\fR.
+This option is an extension.
+.TP
 .B \-n
 Opposite of
 .BR \-v ;
diff --git a/main.c b/main.c
index 4557c57..c6caabc 100644
--- a/main.c
+++ b/main.c
@@ -88,16 +88,17 @@ main(int argc, char **argv)
 	int c;
 	Boolean eoption = 0, woption = 0;
 	const char *driver = 0;
+        const char *fnout = "yy.lex.c";
 
 	sargv = argv;
 	sargc = argc;
 	errorf = stderr;
 	setlocale(LC_CTYPE, "");
+	while ((c = getopt(argc, argv,
 #ifdef DEBUG
-	while ((c = getopt(argc, argv, "dyctvnewVQ:o:")) != EOF) {
-#else
-	while ((c = getopt(argc, argv, "ctvnewVQ:o:")) != EOF) {
+                "dy"
 #endif
+                "ctvneiwVQ:o:")) != EOF) {
 		switch (c) {
 #ifdef DEBUG
 			case 'd':
@@ -149,9 +150,12 @@ main(int argc, char **argv)
 				handleeuc = 1;
 				widecio = 0;
 				break;
+			case 'i':
+				caseless = TRUE;
+				break;
 			default:
 				fprintf(stderr,
-				"Usage: lex [-ewctvnV] [-o outfile] [-Q(y/n)] [file]\n");
+				"Usage: lex [-eiwctvnV] [-o outfile] [-Q(y/n)] [file]\n");
 				exit(1);
 		}
 	}
@@ -172,6 +176,13 @@ main(int argc, char **argv)
 		}
 	} else
 		fin = stdin;
+        if(!fout) {
+                fout = fopen(fnout, "w");
+                if (!fout)
+                        error(
+                        "lex: could not open %s for writing",
+                        fnout);
+        }
 
 	/* may be gotten: def, subs, sname, schar, ccl, dchar */
 	gch();
diff --git a/ncform b/ncform
index a6d8f02..518201e 100644
--- a/ncform
+++ b/ncform
@@ -51,6 +51,11 @@ yylook()
 	register struct yywork *yyt;
 	struct yysvf *yyz;
 	int yych, yyfirst;
+#ifdef LEXCASELESS
+	int yychnc;
+#else
+#define yychnc yych
+#endif
 	struct yywork *yyr;
 # ifdef LEXDEBUG
 	int debug;
@@ -120,8 +125,11 @@ yylook()
 				}
 # endif
 			yyr = yyt;
+#ifdef LEXCASELESS
+                        yychnc = tolower(yych);
+#endif
 			if ( yyt > yycrank){
-				yyt = yyr + yych;
+				yyt = yyr + yychnc;
 				if (yyt <= yytop && yyt->verify+yysvec == yystate){
 					if(yyt->advance+yysvec == YYLERR)	/* error transitions */
 						{unput(*--yylastch);break;}
@@ -139,7 +147,7 @@ yylook()
 # ifdef LEXDEBUG
 				if(debug)fprintf(yyout,"compressed state\n");
 # endif
-				yyt = yyt + yych;
+				yyt = yyt + yychnc;
 				if(yyt <= yytop && yyt->verify+yysvec == yystate){
 					if(yyt->advance+yysvec == YYLERR)	/* error transitions */
 						{unput(*--yylastch);break;}
@@ -150,11 +158,11 @@ yylook()
 					}
 					goto contin;
 					}
-				yyt = yyr + YYU(yymatch[yych]);
+				yyt = yyr + YYU(yymatch[yychnc]);
 # ifdef LEXDEBUG
 				if(debug){
 					fprintf(yyout,"try fall back character ");
-					allprint(YYU(yymatch[yych]));
+					allprint(YYU(yymatch[yychnc]));
 					putchar('\n');
 					}
 # endif
diff --git a/once.h b/once.h
index 44470f5..1c2ebc7 100644
--- a/once.h
+++ b/once.h
@@ -158,6 +158,7 @@ CHR *psave;
 
 Boolean handleeuc = FALSE;
 Boolean widecio = FALSE;
+Boolean caseless = FALSE;
 
 int	isArray = 1;	/* XCU4: for %array %pointer */
 
diff --git a/parser.y b/parser.y
index 893784a..c597cb7 100644
--- a/parser.y
+++ b/parser.y
@@ -132,7 +132,7 @@ defns:	defns STR STR
 			error("Too many definitions");
 		dp += slength($3.cp) + 1;
 		if(dp >= dchar+DEFCHAR)
-			error("Definitions too long");
+			error("Definitions too long (%d)", DEFCHAR);
 		subs[dptr]=def[dptr]=0;	/* for lookup - require ending null */
 	}
 	|
@@ -316,13 +316,19 @@ static int wcwordtos(CHR *ws, char *buf, size_t buflen) {
 static void flex_noyywrap(void) {
 	fprintf(fout, "# define yywrap() 1\n");
 }
+static void flex_caseless(void) {
+	fprintf(fout, "# define LEXCASELESS 1\n");
+	fprintf(fout, "#include <ctype.h>\n");
+	caseless = TRUE;
+}
 static void parse_flex_opts(CHR *p) {
 	static const struct {
-		const char name[9];
+		const char *name;
 		void(*action)(void);
 	} flex_opts[] = {
 		{ "noyywrap", flex_noyywrap},
-		{ {0}, 0 }
+		{ "case-insensitive", flex_caseless},
+		{ 0, 0 }
 	};
 	while(1) {
 		char buf[60+MB_LEN_MAX];
@@ -795,6 +801,7 @@ start:
 				if(prev != '\n')  /* not at line begin, not start */
 					goto character;
 				t = slptr;
+                                x = 0;
 				do {
 					i = 0;
 					if(!isascii(c = gch()))
@@ -857,7 +864,7 @@ start:
 				while((c=gch()) && c != '"' && c != '\n'){
 					if(c == '\\') c = usescape(c=gch());
 					remch(c);
-					token[i++] = c;
+					token[i++] = caseless ? tolower(c) : c;
 					if(i >= TOKENSIZE){
 						warning("String too long");
 						i = TOKENSIZE-1;
@@ -923,8 +930,8 @@ Character range specified between different codesets.");
 						     	     ('0'<=j && k<='9')))
 								warning("Non-portable Character Class");
 							token[i++] = RANGE;
-							token[i++] = j;
-							token[i++] = k;
+							token[i++] = caseless ? tolower(j) : j;
+							token[i++] = caseless ? tolower(k) : k;
 							light = FALSE;
 						} else {
 							error("unmatched hyphen");
@@ -935,7 +942,7 @@ Character range specified between different codesets.");
 					} else {
 						j = c;
 						remch(c);
-						token[i++] = c; /* Remember whatever.*/
+						token[i++] = caseless ? tolower(c) : c; /* Remember whatever.*/
 						light = TRUE;
 						ESCAPE = FALSE;
 					}
@@ -969,9 +976,10 @@ Character range specified between different codesets.");
 				if(alpha(peek)){
 					i = 0;
 					yylval.cp = (CHR *)token;
-					token[i++] = c;
+					token[i++] = caseless ? tolower(c) : c;
 					while(alpha(peek)) {
-						remch(token[i++] = gch());
+                                                c = gch();
+						remch(token[i++] = caseless ? tolower(c) : c);
 						if(i >= TOKENSIZE) {
 							warning("string too long");
 							i = TOKENSIZE - 1;
diff --git a/sub1.c b/sub1.c
index d0e9633..71920d4 100644
--- a/sub1.c
+++ b/sub1.c
@@ -674,14 +674,11 @@ gch(void)
 int
 mn2(int a, intptr_t d, intptr_t c)
 {
-	if (tptr >= treesize) {
+	if (tptr >= treesize || d >= treesize || c >= treesize) {
 		tptr++;
-		error("Parse tree too big %s",
+		error("Parse tree too big (%d) %s", treesize,
 			(treesize == TREESIZE ? "\nTry using %e num" : ""));
 	}
-	if (d >= treesize) {
-		error("Parse error");
-	}
 	name[tptr] = a;
 	left[tptr] = d;
 	right[tptr] = c;
@@ -723,7 +720,7 @@ mn1(int a, intptr_t d)
 {
 	if (tptr >= treesize) {
 		tptr++;
-		error("Parse tree too big %s",
+		error("Parse tree too big (%d) %s", treesize,
 		(treesize == TREESIZE ? "\nTry using %e num" : ""));
 	}
 	name[tptr] = a;
@@ -766,7 +763,7 @@ mn0(int a)
 {
 	if (tptr >= treesize) {
 		tptr++;
-		error("Parse tree too big %s",
+		error("Parse tree too big (%d) %s", treesize,
 			(treesize == TREESIZE ? "\nTry using %e num" : ""));
 	}
 
diff --git a/sub2.c b/sub2.c
index 6a14764..0ae25a3 100644
--- a/sub2.c
+++ b/sub2.c
@@ -93,7 +93,8 @@ cfoll(int v)
 				*pcptr++ = 0;
 				if (pcptr > pchar + pchlen)
 					error(
-					"Too many packed character classes");
+					"Too many packed character classes (%d)",
+                                                pchlen);
 				left[v] = (intptr_t)p;
 				name[v] = RCCL;	/* RNCCL eliminated */
 #ifdef DEBUG
@@ -167,7 +168,7 @@ add(int **array, int n)
 	nxtpos = temp;
 	if (nxtpos >= positions+maxpos)
 		error(
-		"Too many positions %s",
+		"Too many positions (%d) %s", maxpos,
 		(maxpos == MAXPOS ? "\nTry using %p num" : ""));
 }
 
@@ -426,8 +427,8 @@ cgoto(void)
 				else if (xstate == -1) {
 					if (stnum+1 >= nstates) {
 						stnum++;
-						error("Too many states %s",
-						(nstates == NSTATES ?
+						error("Too many states (%d) %s",
+						nstates, (nstates == NSTATES ?
 						"\nTry using %n num":""));
 					}
 					add(state, ++stnum);
@@ -698,6 +699,8 @@ packtrans(int st, CHR *tch, int *tst, int cnt, int tryit)
 #endif
 nopack:
 	/* stick it in */
+                if((nptr+cnt) > ntrans)
+                    goto errntrans;
 		gotof[st] = nptr;
 		nexts[nptr] = cnt;
 		for (i = 0; i < cnt; i++) {
@@ -712,10 +715,12 @@ packtrans(int st, CHR *tch, int *tst, int cnt, int tryit)
 		gotof[st] = -1;
 		nptr--;
 	} else
-		if (nptr > ntrans)
+		if (nptr > ntrans) {
+errntrans:
 			error(
-			"Too many transitions %s",
+			"Too many transitions (%d) %s", ntrans,
 			(ntrans == NTRANS ? "\nTry using %a num" : ""));
+                }
 }
 
 #ifdef DEBUG
@@ -968,7 +973,7 @@ layout(void)
 			do {
 				startup += 1;
 				if (startup > outsize - ZCH)
-					error("output table overflow");
+					error("output table overflow (%d)", outsize);
 				for (j = bot; j <= top; j++) {
 					k = startup+ctable[nchar[j]];
 					if (verify[k])
@@ -995,7 +1000,7 @@ layout(void)
 			do {
 				startup += 1;
 				if (startup > outsize - ZCH)
-					error("output table overflow");
+					error("output table overflow (%d)", outsize);
 				for (j = bot; j <= top; j++) {
 					k = startup + nchar[j];
 					if (verify[k])
@@ -1070,12 +1075,12 @@ layout(void)
 		else
 			fprintf(fout, "0");
 #ifdef DEBUG
-		fprintf(fout, " },\t\t/* state %d */", i);
+		fprintf(fout, " },\n\t/* state %d */", i);
 #endif
-		fprintf(fout, " },\t\t/* state %d */", i);
+		fprintf(fout, " },\n\t/* state %d */", i);
 	}
 	fprintf(fout,
-		"{ 0,\t0,\t0}};\n"
+		"{ 0,\t0,\t0}\n};\n"
 
 	/* put out yymatch */