diff --git a/lib/KorAP/XML/TEI.pm b/lib/KorAP/XML/TEI.pm
index 493fce5..aa8cd0f 100644
--- a/lib/KorAP/XML/TEI.pm
+++ b/lib/KorAP/XML/TEI.pm
@@ -115,11 +115,13 @@
 
  CHECK:
 
+  return '' unless $html;
+
   $html =~ s/<!--.*?-->//g; # remove all comments in actual line
 
   # Remove comment spanning over several lines
   # No closing comment found
-  if ( index($html, '-->') == -1) {
+  if (index($html, '-->') == -1) {
 
     # Opening comment found
     $i = index($html, '<!--');
diff --git a/lib/KorAP/XML/TEI/Zipper.pm b/lib/KorAP/XML/TEI/Zipper.pm
index c479239..3f96370 100644
--- a/lib/KorAP/XML/TEI/Zipper.pm
+++ b/lib/KorAP/XML/TEI/Zipper.pm
@@ -3,6 +3,7 @@
 use warnings;
 use Log::Any qw($log);
 use IO::Compress::Zip qw($ZipError :constants);
+use Scalar::Util 'blessed';
 
 # man IO::Compress::Zip
 # At present three compression methods are supported by IO::Compress::Zip, namely
@@ -69,6 +70,10 @@
 
 # Close stream and reset zipper
 sub close {
+  unless (blessed $_[0]->[1]) {
+    $log->fatal("No opened zip file to close");
+    return;
+  };
   $_[0]->[1]->close;
   @{$_[0]} = ($_[0]->[0]);
 };