diff --git a/java/README.txt b/java/README.txt
index c6933138a7..96b042f19e 100644
--- a/java/README.txt
+++ b/java/README.txt
@@ -437,15 +437,6 @@ and the runtime overhead. An overview of Nano features:
   MessageNano.
 - The 'bytes' type translates to the Java type byte[].
 
-The generated messages are not thread-safe for writes, but may be
-used simultaneously from multiple threads in a read-only manner.
-In other words, an appropriate synchronization mechanism (such as
-a ReadWriteLock) must be used to ensure that a message, its
-ancestors, and descendants are not accessed by any other threads
-while the message is being modified. Field reads, getter methods,
-toByteArray(...), writeTo(...), getCachedSize(), and
-getSerializedSize() are all considered read-only operations.
-
 IMPORTANT: If you have fields with defaults and opt out of accessors
 
 How fields with defaults are serialized has changed. Because we don't
diff --git a/java/src/main/java/com/google/protobuf/nano/ExtendableMessageNano.java b/java/src/main/java/com/google/protobuf/nano/ExtendableMessageNano.java
index 63c8afcbf5..839f21c981 100644
--- a/java/src/main/java/com/google/protobuf/nano/ExtendableMessageNano.java
+++ b/java/src/main/java/com/google/protobuf/nano/ExtendableMessageNano.java
@@ -47,7 +47,7 @@ public abstract class ExtendableMessageNano<M extends ExtendableMessageNano<M>>
     protected List<UnknownFieldData> unknownFieldData;
 
     @Override
-    protected int computeSerializedSize() {
+    public int getSerializedSize() {
         int size = 0;
         int unknownFieldCount = unknownFieldData == null ? 0 : unknownFieldData.size();
         for (int i = 0; i < unknownFieldCount; i++) {
@@ -55,6 +55,7 @@ public abstract class ExtendableMessageNano<M extends ExtendableMessageNano<M>>
             size += CodedOutputByteBufferNano.computeRawVarint32Size(unknownField.tag);
             size += unknownField.bytes.length;
         }
+        cachedSize = size;
         return size;
     }
 
diff --git a/java/src/main/java/com/google/protobuf/nano/MessageNano.java b/java/src/main/java/com/google/protobuf/nano/MessageNano.java
index d6288c9280..82dc6cca56 100644
--- a/java/src/main/java/com/google/protobuf/nano/MessageNano.java
+++ b/java/src/main/java/com/google/protobuf/nano/MessageNano.java
@@ -38,7 +38,7 @@ import java.io.IOException;
  * @author wink@google.com Wink Saville
  */
 public abstract class MessageNano {
-    protected volatile int cachedSize = -1;
+    protected int cachedSize = -1;
 
     /**
      * Get the number of bytes required to encode this message.
@@ -61,18 +61,9 @@ public abstract class MessageNano {
      * using getCachedSize().
      */
     public int getSerializedSize() {
-        int size = computeSerializedSize();
-        cachedSize = size;
-        return size;
-    }
-
-    /**
-     * Computes the number of bytes required to encode this message. This does not update the
-     * cached size.
-     */
-    protected int computeSerializedSize() {
-      // This is overridden if the generated message has serialized fields.
-      return 0;
+        // This is overridden if the generated message has serialized fields.
+        cachedSize = 0;
+        return 0;
     }
 
     /**
diff --git a/java/src/test/java/com/google/protobuf/NanoTest.java b/java/src/test/java/com/google/protobuf/NanoTest.java
index 00e2597edd..9987cacede 100644
--- a/java/src/test/java/com/google/protobuf/NanoTest.java
+++ b/java/src/test/java/com/google/protobuf/NanoTest.java
@@ -105,12 +105,6 @@ public class NanoTest extends TestCase {
     assertEquals(456, newMsg.d);
     assertEquals(2, msg.nestedMsg.bb);
     assertEquals(SimpleMessageNano.BAR, msg.defaultNestedEnum);
-
-    msg.nestedMsg = null;
-    assertTrue(msgSerializedSize != msg.getSerializedSize());
-
-    msg.clear();
-    assertEquals(0, msg.getSerializedSize());
   }
 
   public void testRecursiveMessageNano() throws Exception {
@@ -149,12 +143,6 @@ public class NanoTest extends TestCase {
     assertEquals(3, newMsg.repeatedRecursiveMessageNano[0].id);
   }
 
-  public void testMessageNoFields() {
-    SingleMessageNano msg = new SingleMessageNano();
-    assertEquals(0, msg.getSerializedSize());
-    assertEquals(0, MessageNano.toByteArray(msg).length);
-  }
-
   public void testNanoRequiredInt32() throws Exception {
     TestAllTypesNano msg = new TestAllTypesNano();
     msg.id = 123;
@@ -2910,20 +2898,6 @@ public class NanoTest extends TestCase {
     assertTrue(Arrays.equals(enums, message.getExtension(RepeatedExtensions.repeatedEnum)));
   }
 
-  public void testNullExtensions() throws Exception {
-    // Check that clearing the extension on an empty message is a no-op.
-    Extensions.ExtendableMessage message = new Extensions.ExtendableMessage();
-    message.setExtension(SingularExtensions.someMessage, null);
-    assertEquals(0, MessageNano.toByteArray(message).length);
-
-    // Check that the message is empty after setting and clearing an extension.
-    AnotherMessage another = new AnotherMessage();
-    message.setExtension(SingularExtensions.someMessage, another);
-    assertTrue(MessageNano.toByteArray(message).length > 0);
-    message.setExtension(SingularExtensions.someMessage, null);
-    assertEquals(0, MessageNano.toByteArray(message).length);
-  }
-
   public void testUnknownFields() throws Exception {
     // Check that we roundtrip (serialize and deserialize) unrecognized fields.
     AnotherMessage message = new AnotherMessage();
diff --git a/src/google/protobuf/compiler/javanano/javanano_message.cc b/src/google/protobuf/compiler/javanano/javanano_message.cc
index 0cf9f97102..e0b24b5d36 100644
--- a/src/google/protobuf/compiler/javanano/javanano_message.cc
+++ b/src/google/protobuf/compiler/javanano/javanano_message.cc
@@ -311,8 +311,8 @@ GenerateMessageSerializationMethods(io::Printer* printer) {
   printer->Print(
     "\n"
     "@Override\n"
-    "protected int computeSerializedSize() {\n"
-    "  int size = super.computeSerializedSize();\n");
+    "public int getSerializedSize() {\n"
+    "  int size = super.getSerializedSize();\n");
   printer->Indent();
 
   for (int i = 0; i < descriptor_->field_count(); i++) {
@@ -321,6 +321,7 @@ GenerateMessageSerializationMethods(io::Printer* printer) {
 
   printer->Outdent();
   printer->Print(
+    "  cachedSize = size;\n"
     "  return size;\n"
     "}\n");
 }