diff --git a/src/main/java/org/ids_mannheim/Worker.java b/src/main/java/org/ids_mannheim/Worker.java
index 18a14bd..635934d 100644
--- a/src/main/java/org/ids_mannheim/Worker.java
+++ b/src/main/java/org/ids_mannheim/Worker.java
@@ -88,10 +88,11 @@
                             }
                         }
                     } else if (fold == target_fold) {
-                        String[] strings = line.split("\\s+");
+                        String[] strings = line.split("\\t");
                         if (strings.length < 4) {
                             continue;
                         }
+                        assert strings.length == 10 : "CoNLL-U Format must have 10 columns";
                         if (with_lemma_and_pos) {
                             //noinspection ConstantCondition
                             slidingWindowQueue.add(join("\t", strings[1], strings[2], strings[3]));