diff --git a/PVE/Storage/Plugin.pm b/PVE/Storage/Plugin.pm
index 283eafc..963c391 100644
--- a/PVE/Storage/Plugin.pm
+++ b/PVE/Storage/Plugin.pm
@@ -1115,6 +1115,7 @@ sub read_common_header($) {
     my ($fh) = @_;
     sysread($fh, my $size, 8);
     $size = unpack('Q<', $size);
+    die "import: no size found in export header, aborting.\n" if !defined($size);
     die "got a bad size (not a multiple of 1K)\n" if ($size&1023);
     # Size is in bytes!
     return $size;