diff --git a/config.l b/config.l
index 4a88562..e4ad02e 100644
--- a/config.l
+++ b/config.l
@@ -14,7 +14,7 @@ unsigned int line = 1, col = 0;
 
 %}
 
-NUMBER		[0-9]+
+NUMBER		-?[0-9]+
 VALUE		\".*\"
 MALSTRING	\"[^\"\n]*\n
 WHITE		[\t ]*
@@ -22,7 +22,30 @@ COMMENT		^#.*
 
 %%
 
-{NUMBER} { yylval.i = atoi(yytext); return TYPE_NUMBER; }
+{NUMBER} { 
+  unsigned int x;
+  errno = 0;
+  
+  if (atoi(yytext) < 0)
+  {
+    fprintf(stderr,"%s:%d: negative value not accepted! Fix it now!\n",
+      config, line);
+    graceful_exit(1);
+  }
+  
+  x = strtoul(yytext, NULL, 10);
+  
+  if (errno == ERANGE)
+  {
+    fprintf(stderr, "%s:%d: %s is too big! Fix it now!\n",
+      config, line, yytext);
+    graceful_exit(1);
+  }
+  
+  yylval.i = x;
+  return TYPE_NUMBER;
+}
+
 {VALUE}	{
   yytext[yyleng - 1] = '\0'; /* Kill the trailing quote */
   yylval.s = strdup(yytext + 1); /* kill leading quote */