diff --git a/src/main/java/de/vanitasvitae/imi/codes/InputValidator.java b/src/main/java/de/vanitasvitae/imi/codes/InputValidator.java
index c9641b9..9dba898 100644
--- a/src/main/java/de/vanitasvitae/imi/codes/InputValidator.java
+++ b/src/main/java/de/vanitasvitae/imi/codes/InputValidator.java
@@ -5,17 +5,18 @@ import java.util.regex.Pattern;
 public class InputValidator {
 
     // Allowed characters
-    public static final String ALPHABET = "[a-zA-Z0-9]";
+    public static final String REGEX_ALPHABET = "[a-zA-Z0-9]";
+    public static final String ALPHABET = "abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ0123456789";
 
     /*
     REGEX pattern for study numbers. Allowed are all 3-letter numbers from the alphabet [a-zA-Z0-9].
      */
-    private static final Pattern STUDY_NUMBER_MATCHER = Pattern.compile(ALPHABET+"{3}");
+    private static final Pattern STUDY_NUMBER_MATCHER = Pattern.compile(REGEX_ALPHABET +"{3}");
 
     /*
     REGEX pattern for sample numbers. Allowed are four-letter numbers from the alphabet [a-zA-Z0-9].
      */
-    private static final Pattern SAMPLE_NUMBER_MATCHER = Pattern.compile(ALPHABET+"{4}");
+    private static final Pattern SAMPLE_NUMBER_MATCHER = Pattern.compile(REGEX_ALPHABET +"{4}");
 
     /**
      * Validate a given study number. Valid study numbers are 3-letter codes from the alphabet [a-zA-Z0-9].
diff --git a/src/test/java/de/vanitasvitae/imi/codes/InputValidatorTest.java b/src/test/java/de/vanitasvitae/imi/codes/InputValidatorTest.java
index 47275cc..261615d 100644
--- a/src/test/java/de/vanitasvitae/imi/codes/InputValidatorTest.java
+++ b/src/test/java/de/vanitasvitae/imi/codes/InputValidatorTest.java
@@ -10,8 +10,6 @@ public class InputValidatorTest {
 
     private static final Random RAND = new Random();
 
-    private static final String ALPHABET = "abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ0123456789";
-
     /**
      * Test, whether {@link InputValidator#validateStudyNumber(String)} accepts 3 digit inputs from the allowed alphabet.
      *
@@ -71,7 +69,8 @@ public class InputValidatorTest {
     private static String generateTestStringOfLength(int len) {
         StringBuilder sb = new StringBuilder();
         for (int i = 0; i < len; i++) {
-            sb.append(ALPHABET.charAt(RAND.nextInt(ALPHABET.length())));
+            sb.append(InputValidator.ALPHABET.charAt(
+                    RAND.nextInt(InputValidator.ALPHABET.length())));
         }
 
         return sb.toString();
diff --git a/src/test/java/de/vanitasvitae/imi/codes/SampleTypeTest.java b/src/test/java/de/vanitasvitae/imi/codes/SampleTypeTest.java
index 8580842..4ef5d84 100644
--- a/src/test/java/de/vanitasvitae/imi/codes/SampleTypeTest.java
+++ b/src/test/java/de/vanitasvitae/imi/codes/SampleTypeTest.java
@@ -12,7 +12,7 @@ import org.junit.Test;
  */
 public class SampleTypeTest {
 
-    private static final Pattern SAMPLE_TYPE_VALUE_PATTERN = Pattern.compile(InputValidator.ALPHABET);
+    private static final Pattern SAMPLE_TYPE_VALUE_PATTERN = Pattern.compile(InputValidator.REGEX_ALPHABET);
 
     /**
      * Test, whether all {@link SampleType} names are of length 1 and from the alphabet [a-zA-Z0-9].