diff --git a/runtime/Java/src/org/antlr/v4/runtime/misc/Interval.java b/runtime/Java/src/org/antlr/v4/runtime/misc/Interval.java
index 69f549ba53..d99bd6afa3 100644
--- a/runtime/Java/src/org/antlr/v4/runtime/misc/Interval.java
+++ b/runtime/Java/src/org/antlr/v4/runtime/misc/Interval.java
@@ -6,7 +6,7 @@
 package org.antlr.v4.runtime.misc;
 
 /** An immutable inclusive interval a..b */
-public class Interval {
+public final class Interval {
 	public static final Interval INVALID = new Interval(-1,-2);
 
 	public final int a;