diff --git a/src/main/java/com/typesafe/config/impl/AbstractConfigValue.java b/src/main/java/com/typesafe/config/impl/AbstractConfigValue.java
index 74c1459f..1c3cf7cd 100644
--- a/src/main/java/com/typesafe/config/impl/AbstractConfigValue.java
+++ b/src/main/java/com/typesafe/config/impl/AbstractConfigValue.java
@@ -5,7 +5,7 @@ import com.typesafe.config.ConfigValue;
 
 abstract class AbstractConfigValue implements ConfigValue {
 
-    private ConfigOrigin origin;
+    final private ConfigOrigin origin;
 
     AbstractConfigValue(ConfigOrigin origin) {
         this.origin = origin;
diff --git a/src/main/java/com/typesafe/config/impl/DefaultTransformer.java b/src/main/java/com/typesafe/config/impl/DefaultTransformer.java
index 0d317413..c7bc1815 100644
--- a/src/main/java/com/typesafe/config/impl/DefaultTransformer.java
+++ b/src/main/java/com/typesafe/config/impl/DefaultTransformer.java
@@ -5,7 +5,7 @@ import com.typesafe.config.ConfigValueType;
 /**
  * Default automatic type transformations.
  */
-class DefaultTransformer implements ConfigTransformer {
+final class DefaultTransformer implements ConfigTransformer {
 
     @Override
     public AbstractConfigValue transform(AbstractConfigValue value,
diff --git a/src/main/java/com/typesafe/config/impl/SimpleConfigObject.java b/src/main/java/com/typesafe/config/impl/SimpleConfigObject.java
index 1cca3a6d..5e8e0005 100644
--- a/src/main/java/com/typesafe/config/impl/SimpleConfigObject.java
+++ b/src/main/java/com/typesafe/config/impl/SimpleConfigObject.java
@@ -15,7 +15,7 @@ import com.typesafe.config.ConfigObject;
 import com.typesafe.config.ConfigOrigin;
 import com.typesafe.config.ConfigValue;
 
-class SimpleConfigObject extends AbstractConfigObject {
+final class SimpleConfigObject extends AbstractConfigObject {
 
     // this map should never be modified - assume immutable
     final private Map<String, AbstractConfigValue> value;
diff --git a/src/main/java/com/typesafe/config/impl/TransformedConfigObject.java b/src/main/java/com/typesafe/config/impl/TransformedConfigObject.java
index fd35cc49..d56b8ae5 100644
--- a/src/main/java/com/typesafe/config/impl/TransformedConfigObject.java
+++ b/src/main/java/com/typesafe/config/impl/TransformedConfigObject.java
@@ -6,7 +6,7 @@ import java.util.Set;
 
 import com.typesafe.config.ConfigValue;
 
-class TransformedConfigObject extends AbstractConfigObject {
+final class TransformedConfigObject extends AbstractConfigObject {
 
     final private AbstractConfigObject underlying;