Index: unsigned.c
--- unsigned.c.orig
+++ unsigned.c
@@ -32,6 +32,7 @@ to preserve same.
 */
 #include "xplot.h"
 #include <stdio.h>
+#include <stdlib.h>
 
 #ifdef ultrix
 #define LIBC_ATOI_IS_BROKEN
@@ -57,7 +58,7 @@ char *unsigned_unparse(coord c)
 
   char *r;
   char buf[50];
-  (void) sprintf(buf,"%u",c.u);
+  (void) sprintf(buf,"%lu",c.u);
   r = malloc((unsigned) strlen(buf)+1);
   if (r == 0)
     fatalerror("malloc returned 0");
@@ -68,24 +69,11 @@ char *unsigned_unparse(coord c)
 coord unsigned_parse(char *s)
 {
   coord r;
-#ifndef LIBC_ATOI_IS_BROKEN
-  extern int atoi();
+  const char *errstr;
 
-  r.u = atoi(s);
-#else
-  char *p;
-  r.u = 0;
-  p = s;
-
-  while (isdigit(*p)) {
-    r.u *= 10;
-    r.u += (*p - '0');
-    p++;
-  }
-  if (*p != '\0')
-    fprintf(stderr,"warning: unsigned_parse format error in string: %s\n", s);
-#endif  
-
+  r.u = strtonum(s, 0, ULONG_MAX, &errstr);
+  if (errstr != NULL)
+    fprintf(stderr, "warning: unsigned_parse value is %s: %s\n", errstr, s);
   return r;
 }