diff --git a/lib/KorAP/Indexer.pm b/lib/KorAP/Indexer.pm
index ba65c5b..94503a4 100644
--- a/lib/KorAP/Indexer.pm
+++ b/lib/KorAP/Indexer.pm
@@ -1,5 +1,5 @@
 package KorAP::Indexer;
 
-our $VERSION = 0.02;
+our $VERSION = 0.03;
 
 1;
diff --git a/lib/KorAP/Tokenizer/Units.pm b/lib/KorAP/Tokenizer/Units.pm
index 828711d..8130cb9 100644
--- a/lib/KorAP/Tokenizer/Units.pm
+++ b/lib/KorAP/Tokenizer/Units.pm
@@ -56,6 +56,8 @@
 
   ($from, $to) = $self->_offset($from, $to);
 
+  return if !$to;
+  $from ||= 0;
   return unless $to > $from;
 
   my $pos = $self->match->lookup($from, $to);