diff --git a/gson/src/main/java/com/google/gson/internal/LinkedHashTreeMap.java b/gson/src/main/java/com/google/gson/internal/LinkedHashTreeMap.java
index 7597ef34..44270fc8 100644
--- a/gson/src/main/java/com/google/gson/internal/LinkedHashTreeMap.java
+++ b/gson/src/main/java/com/google/gson/internal/LinkedHashTreeMap.java
@@ -673,7 +673,7 @@ public final class LinkedHashTreeMap<K, V> extends AbstractMap<K, V> implements
    * comparisons. Using this class to create a tree of size <i>S</i> is
    * {@code O(S)}.
    */
-  static class AvlBuilder<K, V> {
+  final static class AvlBuilder<K, V> {
     /** This stack is a singly linked list, linked by the 'parent' field. */
     private Node<K, V> stack;
     private int leavesToSkip;
diff --git a/gson/src/main/java/com/google/gson/internal/Streams.java b/gson/src/main/java/com/google/gson/internal/Streams.java
index ad0b4bf2..607c9293 100644
--- a/gson/src/main/java/com/google/gson/internal/Streams.java
+++ b/gson/src/main/java/com/google/gson/internal/Streams.java
@@ -76,7 +76,7 @@ public final class Streams {
    * Adapts an {@link Appendable} so it can be passed anywhere a {@link Writer}
    * is used.
    */
-  private static class AppendableWriter extends Writer {
+  private static final class AppendableWriter extends Writer {
     private final Appendable appendable;
     private final CurrentWrite currentWrite = new CurrentWrite();
 
diff --git a/gson/src/main/java/com/google/gson/internal/bind/ReflectiveTypeAdapterFactory.java b/gson/src/main/java/com/google/gson/internal/bind/ReflectiveTypeAdapterFactory.java
index 0f5564bd..e64ed17b 100644
--- a/gson/src/main/java/com/google/gson/internal/bind/ReflectiveTypeAdapterFactory.java
+++ b/gson/src/main/java/com/google/gson/internal/bind/ReflectiveTypeAdapterFactory.java
@@ -144,7 +144,7 @@ public final class ReflectiveTypeAdapterFactory implements TypeAdapterFactory {
     abstract void read(JsonReader reader, Object value) throws IOException, IllegalAccessException;
   }
 
-  public final class Adapter<T> extends TypeAdapter<T> {
+  public static final class Adapter<T> extends TypeAdapter<T> {
     private final ObjectConstructor<T> constructor;
     private final Map<String, BoundField> boundFields;