Index: library/Zend/Validate/Isbn.php
===================================================================
--- library/Zend/Validate/Isbn.php	(revision 20329)
+++ library/Zend/Validate/Isbn.php	(working copy)
@@ -102,13 +102,15 @@
         // prepare separator and pattern list
         $sep      = quotemeta($this->_separator);
         $patterns = array();
+        $stringlength = array();
 
         // check for ISBN-10
         if ($this->_type == self::ISBN10 || $this->_type == self::AUTO) {
             if (empty($sep)) {
-                $pattern = '^[0-9]{9}[0-9X]{1}$';
+                $pattern = '/^[0-9]{9}[0-9X]{1}$/';
             } else {
-                $pattern = "^[0-9]{1,7}[{$sep}]{1}[0-9]{1,7}[{$sep}]{1}[0-9]{1,7}[{$sep}]{1}[0-9X]{1}\${13}";
+                $pattern = "/^[0-9]{1,7}[{$sep}]{1}[0-9]{1,7}[{$sep}]{1}[0-9]{1,7}[{$sep}]{1}[0-9X]{1}\$/";
+                $stringlength[$pattern] = 13;
             }
             $patterns[$pattern] = self::ISBN10;
         }
@@ -116,17 +118,23 @@
         // check for ISBN-13
         if ($this->_type == self::ISBN13 || $this->_type == self::AUTO) {
             if (empty($sep)) {
-                $pattern = '^[0-9]{13}$';
+                $pattern = '/^[0-9]{13}$/';
             } else {
-                $pattern = "^[0-9]{1,9}[{$sep}]{1}[0-9]{1,5}[{$sep}]{1}[0-9]{1,9}[{$sep}]{1}[0-9]{1,9}[{$sep}]{1}[0-9]{1}\${17}";
+                $pattern = "/^[0-9]{1,9}[{$sep}]{1}[0-9]{1,5}[{$sep}]{1}[0-9]{1,9}[{$sep}]{1}[0-9]{1,9}[{$sep}]{1}[0-9]{1}\$/";
+                $stringlength[$pattern] = 17;
             }
             $patterns[$pattern] = self::ISBN13;
         }
 
         // check pattern list
         foreach ($patterns as $pattern => $type) {
-            if (ereg($pattern, $this->_value) == 1) {
-                return $type;
+            if (preg_match($pattern, $this->_value) == 1) {
+                if (isset($stringlength[$pattern])
+                    && $stringlength[$pattern] == strlen($this->_value)) {
+                    return $type;
+                } elseif(!isset($stringlength[$pattern])) {
+                    return $type;
+                }
             }
         }
         return null;