Index: Render.pm
===================================================================
--- Render.pm	(revision 3889)
+++ Render.pm	(working copy)
@@ -828,8 +828,10 @@
 
     my $removed = {};    # Map of placeholders to tag parameters and text
 
-    $text =~ s/(\s*<!DOCTYPE.*?>\s*)//is;
-    my $doctype = $1 || '';
+    my $doctype = '';
+    if ($text =~ s/(\s*<!DOCTYPE.*?>\s*)//is) {
+      $doctype = $1;
+    }
 
     $text = $this->takeOutBlocks( $text, 'verbatim', $removed );
     $text = $this->takeOutBlocks( $text, 'head', $removed );