diff --git a/pdfminer/pdfdocument.py b/pdfminer/pdfdocument.py
index c170f1a..4754926 100644
--- a/pdfminer/pdfdocument.py
+++ b/pdfminer/pdfdocument.py
@@ -219,7 +219,7 @@ class PDFXRefStream(PDFBaseXRef):
         if not isinstance(stream, PDFStream) or stream['Type'] is not LITERAL_XREF:
             raise PDFNoValidXRef('Invalid PDF stream spec.')
         size = stream['Size']
-        index_array = stream.get('Index', (1, size))
+        index_array = stream.get('Index', (0, size))
         if len(index_array) % 2 != 0:
             raise PDFSyntaxError('Invalid index number')
         self.ranges.extend(choplist(2, index_array))
diff --git a/pdfminer/pdfinterp.py b/pdfminer/pdfinterp.py
index 788bf8b..2eda0ae 100644
--- a/pdfminer/pdfinterp.py
+++ b/pdfminer/pdfinterp.py
@@ -313,7 +313,7 @@ class PDFPageInterpreter(object):
         return
 
     def dup(self):
-        return PDFPageInterpreter(self.rsrcmgr, self.device)
+        return self.__class__(self.rsrcmgr, self.device)
 
     # init_resources(resources):
     #   Prepare the fonts and XObjects listed in the Resource attribute.