diff -r 1c62c6009161 -r 5e69b1bb707f src/main/java/de/uapcore/sudoku/SudokuTextField.java
--- a/src/main/java/de/uapcore/sudoku/SudokuTextField.java	Mon Jul 27 10:56:17 2020 +0200
+++ b/src/main/java/de/uapcore/sudoku/SudokuTextField.java	Mon Jul 27 11:56:41 2020 +0200
@@ -127,7 +127,7 @@
     public void setValue(int v) {
         if (v == 0) {
             setText("");
-        } else if (v < 10) {
+        } else if (v > 0 && v < 10) {
             setText(String.valueOf(v));
         } else {
             throw new IllegalArgumentException(