diff --git a/src/main/java/com/idealista/fpe/FormatPreservingEncryption.java b/src/main/java/com/idealista/fpe/FormatPreservingEncryption.java
index 7ccf1ee..4a8dfcd 100644
--- a/src/main/java/com/idealista/fpe/FormatPreservingEncryption.java
+++ b/src/main/java/com/idealista/fpe/FormatPreservingEncryption.java
@@ -37,7 +37,7 @@ public String decrypt(String cipherText, byte[] tweak) {
         return selectedDomain.transform(numeralPlainText);
     }
 
-    private void check(String text, byte[] tweak) {
+    protected void check(String text, byte[] tweak) {
         if (text == null || tweak == null)
             throw  new IllegalArgumentException(NULL_INPUT.toString());