diff --git a/lib/KorAP/XML/Tokenizer.pm b/lib/KorAP/XML/Tokenizer.pm
index 3496d69..482bcf7 100644
--- a/lib/KorAP/XML/Tokenizer.pm
+++ b/lib/KorAP/XML/Tokenizer.pm
@@ -116,10 +116,19 @@
   # my (@non_word_tokens);
 
   my $p = $doc->primary;
+  my $old_end = 0;
   foreach my $span (@$tokens) {
     my $from = $span->{'-from'};
     my $to = $span->{'-to'};
 
+    if ($from < $old_end) {
+      $self->error("Tokens duplicated or not in order");
+      $log->warn("Token positions not in order in [$from-$to] in $path");
+      return;
+    };
+
+    $old_end = $to;
+
     # Get the subring from primary data
     my $token = $p->data($from, $to);