--- a/src/urweb.lex	Wed May 20 12:44:28 2015 -0400
+++ b/src/urweb.lex	Thu May 28 10:23:43 2015 -0400
@@ -182,7 +182,7 @@
 ws = [\ \t\012\r];
 intconst = [0-9]+;
 realconst = [0-9]+\.[0-9]*;
-hexconst = 0x[0-9A-F]{1,8};
+hexconst = 0x[0-9A-F]+;
 notags = ([^<{\n(]|(\([^\*<{\n]))+;
 xcom = ([^\-]|(-[^\-]))+;
 oint = [0-9][0-9][0-9];
@@ -542,17 +542,25 @@
 <INITIAL> {id}        => (Tokens.SYMBOL (yytext, pos yypos, pos yypos + size yytext));
 <INITIAL> {cid}       => (Tokens.CSYMBOL (yytext, pos yypos, pos yypos + size yytext));
 
-<INITIAL> {hexconst}  => (case StringCvt.scanString (Int64.scan StringCvt.HEX) (String.extract (yytext, 2, NONE)) of
+<INITIAL> {hexconst}  => (let val digits = String.extract (yytext, 2, NONE)
+                              val v = (StringCvt.scanString (Int64.scan StringCvt.HEX) digits)
+                                      handle Overflow => NONE
+                          in
+                          case v of
                               SOME x => Tokens.INT (x, pos yypos, pos yypos + size yytext)
                             | NONE   => (ErrorMsg.errorAt' (pos yypos, pos yypos)
                                                            ("Expected hexInt, received: " ^ yytext);
-                                         continue ()));
+                                         continue ())
+                         end);
 
-<INITIAL> {intconst}  => (case Int64.fromString yytext of
+<INITIAL> {intconst}  => (let val v = (Int64.fromString yytext) handle Overflow => NONE
+                          in 
+                          case v of
                               SOME x => Tokens.INT (x, pos yypos, pos yypos + size yytext)
                             | NONE   => (ErrorMsg.errorAt' (pos yypos, pos yypos)
                                                            ("Expected int, received: " ^ yytext);
-                                         continue ()));
+                                         continue ())
+                         end);
 <INITIAL> {realconst} => (case Real64.fromString yytext of
                             SOME x => Tokens.FLOAT (x, pos yypos, pos yypos + size yytext)
                           | NONE   => (ErrorMsg.errorAt' (pos yypos, pos yypos)