diff --git a/java/core/BUILD.bazel b/java/core/BUILD.bazel
index b896c42..30c0e90 100644
--- a/java/core/BUILD.bazel
+++ b/java/core/BUILD.bazel
@@ -2,10 +2,10 @@
 load("@rules_java//java:defs.bzl", "java_lite_proto_library", "java_proto_library")
 load("@rules_pkg//:mappings.bzl", "pkg_files", "strip_prefix")
 load("@rules_proto//proto:defs.bzl", "proto_lang_toolchain", "proto_library")
-load("//build_defs:java_opts.bzl", "protobuf_java_export", "protobuf_java_library", "protobuf_versioned_java_library")
-load("//conformance:defs.bzl", "conformance_test")
 load("//:protobuf.bzl", "internal_gen_well_known_protos_java")
 load("//:protobuf_version.bzl", "PROTOBUF_JAVA_VERSION")
+load("//build_defs:java_opts.bzl", "protobuf_java_export", "protobuf_java_library", "protobuf_versioned_java_library")
+load("//conformance:defs.bzl", "conformance_test")
 load("//java/internal:testing.bzl", "junit_tests")
 
 LITE_SRCS = [
@@ -472,6 +472,7 @@
     "src/test/java/com/google/protobuf/FieldPresenceTest.java",
     "src/test/java/com/google/protobuf/ForceFieldBuildersPreRun.java",
     "src/test/java/com/google/protobuf/GeneratedMessageTest.java",
+    "src/test/java/com/google/protobuf/LazilyParsedMessageSetTest.java",
     "src/test/java/com/google/protobuf/LazyFieldTest.java",
     "src/test/java/com/google/protobuf/LazyStringEndToEndTest.java",
     "src/test/java/com/google/protobuf/MapForProto2Test.java",
diff --git a/java/core/src/main/java/com/google/protobuf/FieldSet.java b/java/core/src/main/java/com/google/protobuf/FieldSet.java
index bb3eea9..a8ba1bd 100644
--- a/java/core/src/main/java/com/google/protobuf/FieldSet.java
+++ b/java/core/src/main/java/com/google/protobuf/FieldSet.java
@@ -173,7 +173,8 @@
   /** Get a simple map containing all the fields. */
   public Map<T, Object> getAllFields() {
     if (hasLazyField) {
-      SmallSortedMap<T, Object> result = cloneAllFieldsMap(fields, /* copyList */ false);
+      SmallSortedMap<T, Object> result =
+          cloneAllFieldsMap(fields, /* copyList= */ false, /* resolveLazyFields= */ true);
       if (fields.isImmutable()) {
         result.makeImmutable();
       }
@@ -183,22 +184,22 @@
   }
 
   private static <T extends FieldDescriptorLite<T>> SmallSortedMap<T, Object> cloneAllFieldsMap(
-      SmallSortedMap<T, Object> fields, boolean copyList) {
+      SmallSortedMap<T, Object> fields, boolean copyList, boolean resolveLazyFields) {
     SmallSortedMap<T, Object> result = SmallSortedMap.newFieldMap(DEFAULT_FIELD_MAP_ARRAY_SIZE);
     for (int i = 0; i < fields.getNumArrayEntries(); i++) {
-      cloneFieldEntry(result, fields.getArrayEntryAt(i), copyList);
+      cloneFieldEntry(result, fields.getArrayEntryAt(i), copyList, resolveLazyFields);
     }
     for (Map.Entry<T, Object> entry : fields.getOverflowEntries()) {
-      cloneFieldEntry(result, entry, copyList);
+      cloneFieldEntry(result, entry, copyList, resolveLazyFields);
     }
     return result;
   }
 
   private static <T extends FieldDescriptorLite<T>> void cloneFieldEntry(
-      Map<T, Object> map, Map.Entry<T, Object> entry, boolean copyList) {
+      Map<T, Object> map, Map.Entry<T, Object> entry, boolean copyList, boolean resolveLazyFields) {
     T key = entry.getKey();
     Object value = entry.getValue();
-    if (value instanceof LazyField) {
+    if (resolveLazyFields && value instanceof LazyField) {
       map.put(key, ((LazyField) value).getValue());
     } else if (copyList && value instanceof List) {
       map.put(key, new ArrayList<>((List<?>) value));
@@ -958,7 +959,8 @@
       SmallSortedMap<T, Object> fieldsForBuild = fields;
       if (hasNestedBuilders) {
         // Make a copy of the fields map with all Builders replaced by Message.
-        fieldsForBuild = cloneAllFieldsMap(fields, /* copyList */ false);
+        fieldsForBuild =
+            cloneAllFieldsMap(fields, /* copyList= */ false, /* resolveLazyFields= */ false);
         replaceBuilders(fieldsForBuild, partial);
       }
       FieldSet<T> fieldSet = new FieldSet<>(fieldsForBuild);
@@ -1030,7 +1032,10 @@
 
     /** Returns a new Builder using the fields from {@code fieldSet}. */
     public static <T extends FieldDescriptorLite<T>> Builder<T> fromFieldSet(FieldSet<T> fieldSet) {
-      Builder<T> builder = new Builder<T>(cloneAllFieldsMap(fieldSet.fields, /* copyList */ true));
+      Builder<T> builder =
+          new Builder<T>(
+              cloneAllFieldsMap(
+                  fieldSet.fields, /* copyList= */ true, /* resolveLazyFields= */ false));
       builder.hasLazyField = fieldSet.hasLazyField;
       return builder;
     }
@@ -1040,7 +1045,8 @@
     /** Get a simple map containing all the fields. */
     public Map<T, Object> getAllFields() {
       if (hasLazyField) {
-        SmallSortedMap<T, Object> result = cloneAllFieldsMap(fields, /* copyList */ false);
+        SmallSortedMap<T, Object> result =
+            cloneAllFieldsMap(fields, /* copyList= */ false, /* resolveLazyFields= */ true);
         if (fields.isImmutable()) {
           result.makeImmutable();
         } else {
@@ -1081,7 +1087,7 @@
 
     private void ensureIsMutable() {
       if (!isMutable) {
-        fields = cloneAllFieldsMap(fields, /* copyList */ true);
+        fields = cloneAllFieldsMap(fields, /* copyList= */ true, /* resolveLazyFields= */ false);
         isMutable = true;
       }
     }
diff --git a/java/core/src/test/java/com/google/protobuf/LazilyParsedMessageSetTest.java b/java/core/src/test/java/com/google/protobuf/LazilyParsedMessageSetTest.java
new file mode 100644
index 0000000..c41a381
--- /dev/null
+++ b/java/core/src/test/java/com/google/protobuf/LazilyParsedMessageSetTest.java
@@ -0,0 +1,162 @@
+// Protocol Buffers - Google's data interchange format
+// Copyright 2008 Google Inc.  All rights reserved.
+//
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file or at
+// https://developers.google.com/open-source/licenses/bsd
+
+package com.google.protobuf;
+
+import static com.google.common.truth.Truth.assertThat;
+
+import protobuf_unittest.UnittestMset.RawMessageSet;
+import protobuf_unittest.UnittestMset.TestMessageSetExtension1;
+import protobuf_unittest.UnittestMset.TestMessageSetExtension2;
+import protobuf_unittest.UnittestMset.TestMessageSetExtension3;
+import proto2_wireformat_unittest.UnittestMsetWireFormat.TestMessageSet;
+import org.junit.Before;
+import org.junit.Test;
+import org.junit.runner.RunWith;
+import org.junit.runners.JUnit4;
+
+/** Tests related to handling of MessageSets with lazily parsed extensions. */
+@RunWith(JUnit4.class)
+public class LazilyParsedMessageSetTest {
+  private static final int TYPE_ID_1 =
+      TestMessageSetExtension1.getDescriptor().getExtensions().get(0).getNumber();
+  private static final int TYPE_ID_2 =
+      TestMessageSetExtension2.getDescriptor().getExtensions().get(0).getNumber();
+  private static final int TYPE_ID_3 =
+      TestMessageSetExtension3.getDescriptor().getExtensions().get(0).getNumber();
+  private static final ByteString CORRUPTED_MESSAGE_PAYLOAD =
+      ByteString.copyFrom(new byte[] {(byte) 0xff});
+
+  @Before
+  public void setUp() {
+    ExtensionRegistryLite.setEagerlyParseMessageSets(false);
+  }
+
+  @Test
+  public void testParseAndUpdateMessageSet_unaccessedLazyFieldsAreNotLoaded() throws Exception {
+    ExtensionRegistry extensionRegistry = ExtensionRegistry.newInstance();
+    extensionRegistry.add(TestMessageSetExtension1.messageSetExtension);
+    extensionRegistry.add(TestMessageSetExtension2.messageSetExtension);
+    extensionRegistry.add(TestMessageSetExtension3.messageSetExtension);
+
+    // Set up a TestMessageSet with 2 extensions. The first extension has corrupted payload
+    // data. The test below makes sure that we never load this extension. If we ever do, then we
+    // will handle the exception and replace the value with the default empty message (this behavior
+    // is tested below in testLoadCorruptedLazyField_getsReplacedWithEmptyMessage). Later on we
+    // check that when we serialize the message set, we still have corrupted payload for the first
+    // extension.
+    RawMessageSet inputRaw =
+        RawMessageSet.newBuilder()
+            .addItem(
+                RawMessageSet.Item.newBuilder()
+                    .setTypeId(TYPE_ID_1)
+                    .setMessage(CORRUPTED_MESSAGE_PAYLOAD))
+            .addItem(
+                RawMessageSet.Item.newBuilder()
+                    .setTypeId(TYPE_ID_2)
+                    .setMessage(
+                        TestMessageSetExtension2.newBuilder().setStr("foo").build().toByteString()))
+            .build();
+
+    ByteString inputData = inputRaw.toByteString();
+
+    // Re-parse as a TestMessageSet, so that all extensions are lazy
+    TestMessageSet messageSet = TestMessageSet.parseFrom(inputData, extensionRegistry);
+
+    // Update one extension and add a new one.
+    TestMessageSet.Builder builder = messageSet.toBuilder();
+    builder.setExtension(
+        TestMessageSetExtension2.messageSetExtension,
+        TestMessageSetExtension2.newBuilder().setStr("bar").build());
+
+    // Call .build() in the middle of updating the builder. This triggers a codepath that we want to
+    // make sure preserves lazy fields.
+    TestMessageSet unusedIntermediateMessageSet = builder.build();
+
+    builder.setExtension(
+        TestMessageSetExtension3.messageSetExtension,
+        TestMessageSetExtension3.newBuilder().setRequiredInt(666).build());
+
+    TestMessageSet updatedMessageSet = builder.build();
+
+    // Check that hasExtension call does not load lazy fields.
+    assertThat(updatedMessageSet.hasExtension(TestMessageSetExtension1.messageSetExtension))
+        .isTrue();
+
+    // Serialize. The first extension should still be unloaded and will get serialized using the
+    // same corrupted byte array.
+    ByteString outputData = updatedMessageSet.toByteString();
+
+    // Re-parse as RawMessageSet
+    RawMessageSet actualRaw =
+        RawMessageSet.parseFrom(outputData, ExtensionRegistry.getEmptyRegistry());
+
+    RawMessageSet expectedRaw =
+        RawMessageSet.newBuilder()
+            .addItem(
+                RawMessageSet.Item.newBuilder()
+                    .setTypeId(TYPE_ID_1)
+                    // This is the important part -- we want to make sure that the payload of the
+                    // 1st extensions is the same corrupted byte array. If we ever load the
+                    // extension during our manipulations above, then we would have replaced it with
+                    // the default empty message.
+                    .setMessage(CORRUPTED_MESSAGE_PAYLOAD))
+            .addItem(
+                RawMessageSet.Item.newBuilder()
+                    .setTypeId(TYPE_ID_2)
+                    .setMessage(
+                        TestMessageSetExtension2.newBuilder().setStr("bar").build().toByteString()))
+            .addItem(
+                RawMessageSet.Item.newBuilder()
+                    .setTypeId(TYPE_ID_3)
+                    .setMessage(
+                        TestMessageSetExtension3.newBuilder()
+                            .setRequiredInt(666)
+                            .build()
+                            .toByteString()))
+            .build();
+
+    assertThat(actualRaw).isEqualTo(expectedRaw);
+  }
+
+  @Test
+  public void testLoadCorruptedLazyField_getsReplacedWithEmptyMessage() throws Exception {
+    ExtensionRegistry extensionRegistry = ExtensionRegistry.newInstance();
+    extensionRegistry.add(TestMessageSetExtension1.messageSetExtension);
+
+    RawMessageSet inputRaw =
+        RawMessageSet.newBuilder()
+            .addItem(
+                RawMessageSet.Item.newBuilder()
+                    .setTypeId(TYPE_ID_1)
+                    .setMessage(CORRUPTED_MESSAGE_PAYLOAD))
+            .build();
+
+    ByteString inputData = inputRaw.toByteString();
+
+    // Re-parse as a TestMessageSet, so that all extensions are lazy
+    TestMessageSet messageSet = TestMessageSet.parseFrom(inputData, extensionRegistry);
+
+    assertThat(messageSet.getExtension(TestMessageSetExtension1.messageSetExtension))
+        .isEqualTo(TestMessageSetExtension1.getDefaultInstance());
+
+    // Serialize. The first extension should be serialized as an empty message.
+    ByteString outputData = messageSet.toByteString();
+
+    // Re-parse as RawMessageSet
+    RawMessageSet actualRaw =
+        RawMessageSet.parseFrom(outputData, ExtensionRegistry.getEmptyRegistry());
+
+    RawMessageSet expectedRaw =
+        RawMessageSet.newBuilder()
+            .addItem(
+                RawMessageSet.Item.newBuilder().setTypeId(TYPE_ID_1).setMessage(ByteString.empty()))
+            .build();
+
+    assertThat(actualRaw).isEqualTo(expectedRaw);
+  }
+}
diff --git a/java/core/src/test/java/com/google/protobuf/WireFormatTest.java b/java/core/src/test/java/com/google/protobuf/WireFormatTest.java
index 4afeff8..bbf8d0c 100644
--- a/java/core/src/test/java/com/google/protobuf/WireFormatTest.java
+++ b/java/core/src/test/java/com/google/protobuf/WireFormatTest.java
@@ -12,7 +12,6 @@
 import protobuf_unittest.UnittestMset.RawMessageSet;
 import protobuf_unittest.UnittestMset.TestMessageSetExtension1;
 import protobuf_unittest.UnittestMset.TestMessageSetExtension2;
-import protobuf_unittest.UnittestMset.TestMessageSetExtension3;
 import protobuf_unittest.UnittestProto;
 import protobuf_unittest.UnittestProto.TestAllExtensions;
 import protobuf_unittest.UnittestProto.TestAllTypes;
@@ -506,73 +505,6 @@
         .isEqualTo(123);
   }
 
-  @Test
-  public void testParseAndUpdateMessageSetExtensionEagerly() throws Exception {
-    testParseAndUpdateMessageSetExtensionEagerlyWithFlag(true);
-  }
-
-  @Test
-  public void testParseAndUpdateMessageSetExtensionNotEagerly() throws Exception {
-    testParseAndUpdateMessageSetExtensionEagerlyWithFlag(false);
-  }
-
-  private void testParseAndUpdateMessageSetExtensionEagerlyWithFlag(boolean eagerParsing)
-      throws Exception {
-    ExtensionRegistryLite.setEagerlyParseMessageSets(eagerParsing);
-    ExtensionRegistry extensionRegistry = ExtensionRegistry.newInstance();
-    extensionRegistry.add(TestMessageSetExtension1.messageSetExtension);
-    extensionRegistry.add(TestMessageSetExtension2.messageSetExtension);
-    extensionRegistry.add(TestMessageSetExtension3.messageSetExtension);
-
-    // Set up a RawMessageSet with 2 extensions
-    RawMessageSet raw =
-        RawMessageSet.newBuilder()
-            .addItem(
-                RawMessageSet.Item.newBuilder()
-                    .setTypeId(TYPE_ID_1)
-                    .setMessage(
-                        TestMessageSetExtension1.newBuilder().setI(123).build().toByteString())
-                    .build())
-            .addItem(
-                RawMessageSet.Item.newBuilder()
-                    .setTypeId(TYPE_ID_2)
-                    .setMessage(
-                        TestMessageSetExtension2.newBuilder().setStr("foo").build().toByteString())
-                    .build())
-            .build();
-
-    ByteString data = raw.toByteString();
-
-    // Parse as a TestMessageSet.
-    TestMessageSet messageSet = TestMessageSet.parseFrom(data, extensionRegistry);
-
-    // Update one extension and add a new one.
-    TestMessageSet.Builder builder = messageSet.toBuilder();
-    builder.setExtension(
-        TestMessageSetExtension2.messageSetExtension,
-        TestMessageSetExtension2.newBuilder().setStr("bar").build());
-    builder.setExtension(
-        TestMessageSetExtension3.messageSetExtension,
-        TestMessageSetExtension3.newBuilder().setRequiredInt(666).build());
-
-    TestMessageSet updatedMessageSet = builder.build();
-    // Check all 3 extensions
-    assertThat(updatedMessageSet.getExtension(TestMessageSetExtension1.messageSetExtension).getI())
-        .isEqualTo(123);
-    assertThat(
-            updatedMessageSet.getExtension(TestMessageSetExtension2.messageSetExtension).getStr())
-        .isEqualTo("bar");
-    assertThat(
-            updatedMessageSet
-                .getExtension(TestMessageSetExtension3.messageSetExtension)
-                .getRequiredInt())
-        .isEqualTo(666);
-
-    // Serialize and re-parse, and make sure we get the same message back
-    assertThat(TestMessageSet.parseFrom(updatedMessageSet.toByteString(), extensionRegistry))
-        .isEqualTo(updatedMessageSet);
-  }
-
   // ================================================================
   // oneof
   @Test