# tests / unwrap
                        reEncodedHeader = re.compile(self.XMP_HEADER_PATTERN.encode(self.encoding))
                        m = reEncodedHeader.match(packet)
-                       assert m is not None, "No xmp header found"
-                       xmp = packet[m.end():]
+                       if m is None :
+                               console.warn('XMP packet wrapper not found')
+                               self.xmp = packet
+                               return
 
+                       xmp = packet[m.end():]
                        trailer = self.XMP_TRAILER[:-6].encode(self.encoding)  # TODO handle read-only mode
                        trailerPos = xmp.find(trailer)
                        assert trailerPos != -1, "No xmp trailer found"