diff --git a/src/config.c b/src/config.c
index e280bd4f..637e4f3c 100644
--- a/src/config.c
+++ b/src/config.c
@@ -288,9 +288,15 @@ void free_tokens(int n, ...)
 
 
 TOKEN *new_number(const char *text) {
+  const char *errstr;
   struct token_t *tkn = new_token(TKN_NUMBER);
   tkn->value.type   = V_NUM;
-  tkn->value.number = atoi(text);
+  tkn->value.number = str_int(text, STR_INT32, &errstr);
+  if(errstr) {
+    yyerror("integer %s in config file: %s", text, errstr);
+    free_token(tkn);
+    return NULL;
+  }
 
 #if DEBUG
   msg_info("NUMBER(%d)\n", tkn->value.number);
@@ -300,31 +306,18 @@ TOKEN *new_number(const char *text) {
 }
 
 TOKEN *new_number_real(const char *text) {
+  char *endptr;
   struct token_t * tkn = new_token(TKN_NUMBER);
   tkn->value.type   = V_NUM_REAL;
-  tkn->value.number_real = atof(text);
-
-#if DEBUG
-  msg_info("NUMBER(%g)\n", tkn->value.number_real);
-#endif
-
-  return tkn;
-}
-
-TOKEN *new_hexnumber(const char *text) {
-  struct token_t *tkn = new_token(TKN_NUMBER);
-  char * e;
-
-  tkn->value.type   = V_NUM;
-  tkn->value.number = strtoul(text, &e, 16);
-  if ((e == text) || (*e != 0)) {
-    yyerror("cannot scan hex number %s", text);
+  tkn->value.number_real = strtod(text, &endptr);
+  if(endptr == text || *endptr) {
+    yyerror("real number in config file %s: parsing error", text);
     free_token(tkn);
     return NULL;
   }
-  
+
 #if DEBUG
-  msg_info("HEXNUMBER(%d)\n", tkn->value.number);
+  msg_info("NUMBER(%g)\n", tkn->value.number_real);
 #endif
 
   return tkn;
diff --git a/src/config.h b/src/config.h
index 0f10f801..6495e40c 100644
--- a/src/config.h
+++ b/src/config.h
@@ -128,8 +128,6 @@ TOKEN *new_number(const char *text);
 
 TOKEN *new_number_real(const char *text);
 
-TOKEN *new_hexnumber(const char *text);
-
 TOKEN *new_constant(const char *text);
 
 TOKEN *new_string(const char *text);
diff --git a/src/lexer.l b/src/lexer.l
index 7b811bad..7d79168f 100644
--- a/src/lexer.l
+++ b/src/lexer.l
@@ -20,7 +20,6 @@
 /* $Id$ */
 
 %{
-/* need this for the call to atof() below */
 #include <math.h>
 #include <string.h>
 #include <errno.h>
@@ -50,9 +49,27 @@ static void adjust_cfg_lineno(const char *p) {
 
 %}
 
-DIGIT    [0-9]
-HEXDIGIT [0-9a-fA-F]
-SIGN     [+-]
+  // AVRDUDE integer size suffix (LL/L/S/H/HH)
+SIZS ([lL][lL]|[lL]|[sS]|[hH]|[hH][hH])
+ // AVRDUDE integer suffix incl unsigned designator
+ISUF ([uU]|[uU]{SIZS}|{SIZS}[uU]|{SIZS})
+ // Non-negative integers
+INUM (0|[1-9][0-9]*){ISUF}?
+ // Octal integers
+ONUM 0[0-7]+{ISUF}?
+ // Binary integers
+BNUM 0[bB][01]+{ISUF}?
+ // Hexadecimal integers - fractional hexadecimals are treated below
+XNUM 0[xX][0-9A-Fa-f]+{ISUF}?
+RNUM (M{0,3})(D?C{0,3}|CM|CD)(L?X{0,3}|XC|XL)(V?I{0,3}|IX|IV)
+
+ // Real numbers (decimal and hexadecimal fractional numbers)
+SIGN [+-]
+DNUM (([0-9]+[eE][-+]?[0-9]+)|([0-9]*\.[0-9]+([eE][-+]?[0-9]+)?))
+HNUM (0[xX](([0-9A-Fa-f]+([pP][-+]?[0-9]+))|([0-9A-Fa-f]*\.[0-9A-Fa-f]+([pP][-+]?[0-9]+)?)))
+NAN  [Nn][Aa][Nn]
+INF  [Ii][Nn][Ff]([Ii][Nn][Ii][Tt][Yy])?
+
 
 %option nounput
 
@@ -63,9 +80,21 @@ SIGN     [+-]
 
 %%
 
-{DIGIT}+                   { yylval = new_number(yytext); return TKN_NUMBER; /* sign is treated in grammar */ }
-{SIGN}?{DIGIT}+"."{DIGIT}* { yylval = new_number_real(yytext); return TKN_NUMBER_REAL; }
-{SIGN}?"."{DIGIT}+         { yylval = new_number_real(yytext); return TKN_NUMBER_REAL; }
+({INUM}|{BNUM}|{ONUM}|{XNUM}|{RNUM}) { /* sign is treated in grammar */
+  yylval = new_number(yytext);
+  if(!yylval)
+    return YYERRCODE;
+
+  return TKN_NUMBER;
+}
+
+{SIGN}?({DNUM}|{HNUM}|{NAN}|{INF}) {
+  yylval = new_number_real(yytext);
+  if(!yylval)
+    return YYERRCODE;
+
+  return TKN_NUMBER_REAL;
+}
 
 ["]([^"\\\n]|\\.|\\\n)*["] {
   char *str= cfg_strdup("lexer.l", yytext);
@@ -78,8 +107,6 @@ SIGN     [+-]
   return TKN_STRING;
 }
 
-0x{HEXDIGIT}+ { yylval = new_hexnumber(yytext); return TKN_NUMBER; }
-
 #\n#\ PROGRAMMER\ DEFINITIONS\n#\n+ { /* Record comments so far as prologue and skip */
   cfg_capture_prologue();
   adjust_cfg_lineno(yytext);