--- data.c.orig	2009-06-21 13:38:14.000000000 +0900
+++ data.c	2009-10-25 03:35:54.414697700 +0900
@@ -2392,17 +2392,43 @@
     val = make_float (sign * atof (p));
   else
     {
-      double v = 0;
+      unsigned char *old_p = p;
+      EMACS_INT most_fixnum, chknum, v = 0;
+      int overflow = 0;		/* most_fixnum overflow */
 
-      while (1)
+      most_fixnum = sign > 0 ? MOST_POSITIVE_FIXNUM : MOST_NEGATIVE_FIXNUM * -1;
+      chknum = most_fixnum / b;
+
+      while (v >= 0)
 	{
 	  int digit = digit_to_number (*p++, b);
 	  if (digit < 0)
 	    break;
+	  if (chknum < v / b)
+	    {
+	      overflow = 1;
+	      break;
+	    }
 	  v = v * b + digit;
 	}
 
-      val = make_fixnum_or_float (sign * v);
+      if (!overflow && v <= most_fixnum && v >= 0)
+	val = make_number (sign * v);
+      else
+	{
+	  double w = 0;
+	  p = old_p;
+
+	  while (1)
+	    {
+	      int digit = digit_to_number (*p++, b);
+	      if (digit < 0)
+		break;
+	      w = w * b + digit;
+	    }
+
+	  val = make_float (sign * w);
+	}
     }
 
   return val;