diff --git a/flink-queryable-state/flink-queryable-state-client-java/src/main/java/org/apache/flink/queryablestate/client/state/serialization/KvStateSerializer.java b/flink-queryable-state/flink-queryable-state-client-java/src/main/java/org/apache/flink/queryablestate/client/state/serialization/KvStateSerializer.java
index 4a64678e5508a..cca630c1481a1 100644
--- a/flink-queryable-state/flink-queryable-state-client-java/src/main/java/org/apache/flink/queryablestate/client/state/serialization/KvStateSerializer.java
+++ b/flink-queryable-state/flink-queryable-state-client-java/src/main/java/org/apache/flink/queryablestate/client/state/serialization/KvStateSerializer.java
@@ -35,6 +35,8 @@
  */
 public final class KvStateSerializer {
 
+	//The magic number is as a flag between key and namespace.
+	private static final int MAGIC_NUMBER = 42;
 	// ------------------------------------------------------------------------
 	// Generic serialization utils
 	// ------------------------------------------------------------------------
@@ -63,7 +65,7 @@ public static <K, N> byte[] serializeKeyAndNamespace(
 		DataOutputSerializer dos = new DataOutputSerializer(32);
 
 		keySerializer.serialize(key, dos);
-		dos.writeByte(42);
+		dos.writeByte(MAGIC_NUMBER);
 		namespaceSerializer.serialize(namespace, dos);
 
 		return dos.getCopyOfBuffer();
@@ -93,7 +95,7 @@ public static <K, N> Tuple2<K, N> deserializeKeyAndNamespace(
 		try {
 			K key = keySerializer.deserialize(dis);
 			byte magicNumber = dis.readByte();
-			if (magicNumber != 42) {
+			if (magicNumber != MAGIC_NUMBER) {
 				throw new IOException("Unexpected magic number " + magicNumber + ".");
 			}
 			N namespace = namespaceSerializer.deserialize(dis);