diff --git a/main/src/main/java/sbt/internal/FlatLoader.java b/main/src/main/java/sbt/internal/FlatLoader.java
index e1586d8be..0c0b9682f 100644
--- a/main/src/main/java/sbt/internal/FlatLoader.java
+++ b/main/src/main/java/sbt/internal/FlatLoader.java
@@ -10,7 +10,7 @@ package sbt.internal;
 import java.net.URL;
 import java.net.URLClassLoader;
 
-class FlatLoader extends URLClassLoader {
+final class FlatLoader extends URLClassLoader {
   static {
     ClassLoader.registerAsParallelCapable();
   }
diff --git a/main/src/main/java/sbt/internal/LayeredClassLoader.java b/main/src/main/java/sbt/internal/LayeredClassLoader.java
index 241f94a05..798e5aa18 100644
--- a/main/src/main/java/sbt/internal/LayeredClassLoader.java
+++ b/main/src/main/java/sbt/internal/LayeredClassLoader.java
@@ -11,7 +11,7 @@ import java.io.File;
 import scala.collection.immutable.Map;
 import scala.collection.Seq;
 
-class LayeredClassLoader extends LayeredClassLoaderImpl {
+final class LayeredClassLoader extends LayeredClassLoaderImpl {
   LayeredClassLoader(
       final Seq<File> classpath,
       final ClassLoader parent,
diff --git a/main/src/main/java/sbt/internal/ResourceLoader.java b/main/src/main/java/sbt/internal/ResourceLoader.java
index b408252d7..9d7993c64 100644
--- a/main/src/main/java/sbt/internal/ResourceLoader.java
+++ b/main/src/main/java/sbt/internal/ResourceLoader.java
@@ -11,7 +11,7 @@ import java.io.File;
 import scala.collection.immutable.Map;
 import scala.collection.Seq;
 
-class ResourceLoader extends ResourceLoaderImpl {
+final class ResourceLoader extends ResourceLoaderImpl {
   ResourceLoader(
       final Seq<File> classpath, final ClassLoader parent, final Map<String, String> resources) {
     super(classpath, parent, resources);