diff --git a/NEWS b/NEWS
index feadcb10..f4cc74b1 100644
--- a/NEWS
+++ b/NEWS
@@ -18,6 +18,8 @@ NEWS ( CHANGELOG and HISTORY )                                     HTMLPurifier
 - Configuration objects with different serials do not clobber each
   others when revision numbers are unequal
 - Improve Serializer DefinitionCache directory permissions checks
+- DefinitionCache no longer throws errors when it encounters old
+  serial files that do not conform to the current style
 . Rewire some test-cases to swallow errors rather than expect them
 . HTMLDefinition printer updated with some of the new attributes
 . DefinitionCache keys reordered to reflect precedence: version number,
diff --git a/library/HTMLPurifier/DefinitionCache.php b/library/HTMLPurifier/DefinitionCache.php
index f21b0354..da18bff3 100644
--- a/library/HTMLPurifier/DefinitionCache.php
+++ b/library/HTMLPurifier/DefinitionCache.php
@@ -49,6 +49,7 @@ class HTMLPurifier_DefinitionCache
      * @param $config Instance of HTMLPurifier_Config to test against
      */
     function isOld($key, $config) {
+        if (substr_count($key, '-') < 3) return true;
         list($version, $hash, $revision) = explode('-', $key, 3);
         $compare = version_compare($version, $config->version);
         // version mismatch, is always old