diff --git a/lexor.lex b/lexor.lex
index fff24e95c..6a93cc283 100644
--- a/lexor.lex
+++ b/lexor.lex
@@ -294,6 +294,7 @@ W [ \t\b\f\r]+
 
 [0-9][0-9_]* {
       yylval.number = make_unsized_dec(yytext);
+      based_size = yylval.number->as_ulong();
       return DEC_NUMBER; }
 
 [0-9][0-9_]*\.[0-9][0-9_]*([Ee][+-]?[0-9][0-9_]*)? {
@@ -462,6 +463,9 @@ static verinum*make_unsized_binary(const char*txt)
       for (const char*idx = ptr ;  *idx ;  idx += 1)
 	    if (*idx != '_') size += 1;
 
+      if ((based_size > 0) && (size > based_size)) yywarn(yylloc,
+          "extra digits given for sized binary constant.");
+
       verinum::V*bits = new verinum::V[size];
 
       unsigned idx = size;
@@ -517,6 +521,13 @@ static verinum*make_unsized_octal(const char*txt)
       for (const char*idx = ptr ;  *idx ;  idx += 1)
 	    if (*idx != '_') size += 3;
 
+      if (based_size > 0) {
+            int rem = based_size % 3;
+	    if (rem != 0) based_size += 3 - rem;
+	    if (size > based_size) yywarn(yylloc,
+	        "extra digits given for sized octal constant.");
+      }
+
       verinum::V*bits = new verinum::V[size];
 
       unsigned idx = size;
@@ -576,6 +587,13 @@ static verinum*make_unsized_hex(const char*txt)
       for (const char*idx = ptr ;  *idx ;  idx += 1)
 	    if (*idx != '_') size += 4;
 
+      if (based_size > 0) {
+            int rem = based_size % 4;
+	    if (rem != 0) based_size += 4 - rem;
+	    if (size > based_size) yywarn(yylloc,
+	        "extra digits given for sized hex constant.");
+      }
+
       verinum::V*bits = new verinum::V[size];
 
       unsigned idx = size;
@@ -803,6 +821,10 @@ static verinum*make_unsized_dec(const char*ptr)
 	    assert(size <= tmp_size);
       }
 
+        /* Since we never have the real number of bits that a decimal
+           number represents we do not check for extra bits. */
+//      if (based_size > 0) { }
+
       verinum*res = new verinum(bits, size, false);
       res->has_sign(signed_flag);
 
diff --git a/parse.y b/parse.y
index 91f435d50..f1a56c7df 100644
--- a/parse.y
+++ b/parse.y
@@ -274,11 +274,12 @@ source_file
 	;
 
 number  : BASED_NUMBER
-	     { $$ = $1; }
+	     { $$ = $1; based_size = 0;}
         | DEC_NUMBER
-	     { $$ = $1; }
+	     { $$ = $1; based_size = 0;}
         | DEC_NUMBER BASED_NUMBER
-	     { $$ = pform_verinum_with_size($1,$2, @2.text, @2.first_line); }
+	     { $$ = pform_verinum_with_size($1,$2, @2.text, @2.first_line);
+	       based_size = 0; }
 	;
 
   /* Verilog-2001 supports attribute lists, which can be attached to a
diff --git a/parse_misc.cc b/parse_misc.cc
index 120f2f4ed..60bd8b02e 100644
--- a/parse_misc.cc
+++ b/parse_misc.cc
@@ -28,6 +28,7 @@
 extern const char*vl_file;
 unsigned error_count = 0;
 unsigned warn_count = 0;
+unsigned long based_size = 0;
 
 void VLerror(const char*msg)
 {
@@ -42,6 +43,7 @@ void VLerror(const YYLTYPE&loc, const char*msg)
 	    cerr << loc.text << ":";
 
       cerr << loc.first_line << ": " << msg << endl;
+      based_size = 0; /* Clear the base information if we have an error. */
 }
 
 void yywarn(const YYLTYPE&loc, const char*msg)
@@ -58,33 +60,3 @@ int VLwrap()
       return -1;
 }
 
-/*
- * $Log: parse_misc.cc,v $
- * Revision 1.7  2002/08/12 01:35:00  steve
- *  conditional ident string using autoconfig.
- *
- * Revision 1.6  2002/06/06 18:57:18  steve
- *  Use standard name for iostream.
- *
- * Revision 1.5  2001/07/25 03:10:49  steve
- *  Create a config.h.in file to hold all the config
- *  junk, and support gcc 3.0. (Stephan Boettcher)
- *
- * Revision 1.4  2000/02/23 02:56:55  steve
- *  Macintosh compilers do not support ident.
- *
- * Revision 1.3  1999/09/29 21:15:31  steve
- *  Standardize formatting of warning messages.
- *
- * Revision 1.2  1998/11/07 17:05:05  steve
- *  Handle procedural conditional, and some
- *  of the conditional expressions.
- *
- *  Elaborate signals and identifiers differently,
- *  allowing the netlist to hold signal information.
- *
- * Revision 1.1  1998/11/03 23:29:02  steve
- *  Introduce verilog to CVS.
- *
- */
-
diff --git a/parse_misc.h b/parse_misc.h
index 2bc10b01a..9f3274689 100644
--- a/parse_misc.h
+++ b/parse_misc.h
@@ -55,33 +55,6 @@ extern void VLerror(const YYLTYPE&loc, const char*msg);
 extern void VLwarn(const YYLTYPE&loc, const char*msg);
 
 extern unsigned error_count, warn_count;
+extern unsigned long based_size;
 
-/*
- * $Log: parse_misc.h,v $
- * Revision 1.7  2003/03/08 20:58:18  steve
- *  More C-like use of vlltype.
- *
- * Revision 1.6  2002/11/03 20:36:53  steve
- *  Support old/new bison yylloc.
- *
- * Revision 1.5  2002/08/12 01:35:00  steve
- *  conditional ident string using autoconfig.
- *
- * Revision 1.4  2000/02/23 02:56:55  steve
- *  Macintosh compilers do not support ident.
- *
- * Revision 1.3  1999/07/10 01:03:18  steve
- *  remove string from lexical phase.
- *
- * Revision 1.2  1998/11/07 17:05:05  steve
- *  Handle procedural conditional, and some
- *  of the conditional expressions.
- *
- *  Elaborate signals and identifiers differently,
- *  allowing the netlist to hold signal information.
- *
- * Revision 1.1  1998/11/03 23:29:03  steve
- *  Introduce verilog to CVS.
- *
- */
 #endif