diff --git a/java/core/src/main/java/com/google/protobuf/Descriptors.java b/java/core/src/main/java/com/google/protobuf/Descriptors.java
index d42a93aac3c3..df36ce4a37e4 100644
--- a/java/core/src/main/java/com/google/protobuf/Descriptors.java
+++ b/java/core/src/main/java/com/google/protobuf/Descriptors.java
@@ -29,6 +29,7 @@
 import com.google.protobuf.DescriptorProtos.OneofOptions;
 import com.google.protobuf.DescriptorProtos.ServiceDescriptorProto;
 import com.google.protobuf.DescriptorProtos.ServiceOptions;
+import com.google.protobuf.Descriptors.DescriptorValidationException;
 import com.google.protobuf.JavaFeaturesProto.JavaFeatures;
 import java.lang.ref.ReferenceQueue;
 import java.lang.ref.WeakReference;
@@ -618,14 +619,18 @@ private FileDescriptor(
     }
 
     public void resolveAllFeaturesImmutable() {
-      resolveAllFeaturesInternal();
+      try {
+        resolveAllFeaturesInternal();
+      } catch (DescriptorValidationException e) {
+        throw new IllegalArgumentException("Invalid features for \"" + proto.getName() + "\".", e);
+      }
     }
 
     /**
      * This method is to be called by generated code only. It resolves features for the descriptor
      * and all of its children.
      */
-    private void resolveAllFeaturesInternal() {
+    private void resolveAllFeaturesInternal() throws DescriptorValidationException {
       if (this.features != null) {
         return;
       }
@@ -712,22 +717,26 @@ private void crossLink() throws DescriptorValidationException {
     private synchronized void setProto(final FileDescriptorProto proto) {
       this.proto = proto;
       this.options = null;
-      this.features = resolveFeatures(proto.getOptions().getFeatures());
+      try {
+        this.features = resolveFeatures(proto.getOptions().getFeatures());
 
-      for (int i = 0; i < messageTypes.length; i++) {
-        messageTypes[i].setProto(proto.getMessageType(i));
-      }
+        for (int i = 0; i < messageTypes.length; i++) {
+          messageTypes[i].setProto(proto.getMessageType(i));
+        }
 
-      for (int i = 0; i < enumTypes.length; i++) {
-        enumTypes[i].setProto(proto.getEnumType(i));
-      }
+        for (int i = 0; i < enumTypes.length; i++) {
+          enumTypes[i].setProto(proto.getEnumType(i));
+        }
 
-      for (int i = 0; i < services.length; i++) {
-        services[i].setProto(proto.getService(i));
-      }
+        for (int i = 0; i < services.length; i++) {
+          services[i].setProto(proto.getService(i));
+        }
 
-      for (int i = 0; i < extensions.length; i++) {
-        extensions[i].setProto(proto.getExtension(i));
+        for (int i = 0; i < extensions.length; i++) {
+          extensions[i].setProto(proto.getExtension(i));
+        }
+      } catch (DescriptorValidationException e) {
+        throw new IllegalArgumentException("Invalid features for \"" + proto.getName() + "\".", e);
       }
     }
   }
@@ -1102,7 +1111,7 @@ private Descriptor(
     }
 
     /** See {@link FileDescriptor#resolveAllFeatures}. */
-    private void resolveAllFeatures() {
+    private void resolveAllFeatures() throws DescriptorValidationException {
       this.features = resolveFeatures(proto.getOptions().getFeatures());
 
       for (Descriptor nestedType : nestedTypes) {
@@ -1162,7 +1171,7 @@ private void validateNoDuplicateFieldNumbers() throws DescriptorValidationExcept
     }
 
     /** See {@link FileDescriptor#setProto}. */
-    private void setProto(final DescriptorProto proto) {
+    private void setProto(final DescriptorProto proto) throws DescriptorValidationException {
       this.proto = proto;
       this.options = null;
       this.features = resolveFeatures(proto.getOptions().getFeatures());
@@ -1327,7 +1336,9 @@ public boolean isRequired() {
 
     /** Is this field declared optional? */
     public boolean isOptional() {
-      return proto.getLabel() == FieldDescriptorProto.Label.LABEL_OPTIONAL;
+      return proto.getLabel() == FieldDescriptorProto.Label.LABEL_OPTIONAL
+          && this.features.getFieldPresence()
+              != DescriptorProtos.FeatureSet.FieldPresence.LEGACY_REQUIRED;
     }
 
     /** Is this field declared repeated? */
@@ -1732,7 +1743,7 @@ private FieldDescriptor(
     }
 
     /** See {@link FileDescriptor#resolveAllFeatures}. */
-    private void resolveAllFeatures() {
+    private void resolveAllFeatures() throws DescriptorValidationException {
       this.features = resolveFeatures(proto.getOptions().getFeatures());
     }
 
@@ -1791,6 +1802,19 @@ boolean hasInferredLegacyProtoFeatures() {
       return false;
     }
 
+    @Override
+    void validateFeatures(FeatureSet features) throws DescriptorValidationException {
+      if (containingType != null
+          && containingType.toProto().getOptions().getMessageSetWireFormat()) {
+        if (isExtension()) {
+          if (!isOptional() || getType() != Type.MESSAGE) {
+            throw new DescriptorValidationException(
+                this, "Extensions of MessageSets must be optional messages.");
+          }
+        }
+      }
+    }
+
     /** Look up and cross-link all field types, etc. */
     private void crossLink() throws DescriptorValidationException {
       if (proto.hasExtendee()) {
@@ -1962,23 +1986,10 @@ private void crossLink() throws DescriptorValidationException {
           }
         }
       }
-
-      if (containingType != null
-          && containingType.toProto().getOptions().getMessageSetWireFormat()) {
-        if (isExtension()) {
-          if (!isOptional() || getType() != Type.MESSAGE) {
-            throw new DescriptorValidationException(
-                this, "Extensions of MessageSets must be optional messages.");
-          }
-        } else {
-          throw new DescriptorValidationException(
-              this, "MessageSets cannot have fields, only extensions.");
-        }
-      }
     }
 
     /** See {@link FileDescriptor#setProto}. */
-    private void setProto(final FieldDescriptorProto proto) {
+    private void setProto(final FieldDescriptorProto proto) throws DescriptorValidationException {
       this.proto = proto;
       this.options = null;
       this.features = resolveFeatures(proto.getOptions().getFeatures());
@@ -2250,7 +2261,7 @@ private EnumDescriptor(
     }
 
     /** See {@link FileDescriptor#resolveAllFeatures}. */
-    private void resolveAllFeatures() {
+    private void resolveAllFeatures() throws DescriptorValidationException {
       this.features = resolveFeatures(proto.getOptions().getFeatures());
       for (EnumValueDescriptor value : values) {
         value.resolveAllFeatures();
@@ -2258,7 +2269,7 @@ private void resolveAllFeatures() {
     }
 
     /** See {@link FileDescriptor#setProto}. */
-    private void setProto(final EnumDescriptorProto proto) {
+    private void setProto(final EnumDescriptorProto proto) throws DescriptorValidationException {
       this.proto = proto;
       this.options = null;
       this.features = resolveFeatures(proto.getOptions().getFeatures());
@@ -2402,12 +2413,13 @@ private EnumValueDescriptor(final EnumDescriptor parent, final Integer number) {
     }
 
     /** See {@link FileDescriptor#resolveAllFeatures}. */
-    private void resolveAllFeatures() {
+    private void resolveAllFeatures() throws DescriptorValidationException {
       this.features = resolveFeatures(proto.getOptions().getFeatures());
     }
 
     /** See {@link FileDescriptor#setProto}. */
-    private void setProto(final EnumValueDescriptorProto proto) {
+    private void setProto(final EnumValueDescriptorProto proto)
+        throws DescriptorValidationException {
       this.proto = proto;
       this.options = null;
       this.features = resolveFeatures(proto.getOptions().getFeatures());
@@ -2517,7 +2529,7 @@ private ServiceDescriptor(
     }
 
     /** See {@link FileDescriptor#resolveAllFeatures}. */
-    private void resolveAllFeatures() {
+    private void resolveAllFeatures() throws DescriptorValidationException {
       this.features = resolveFeatures(proto.getOptions().getFeatures());
 
       for (MethodDescriptor method : methods) {
@@ -2532,7 +2544,7 @@ private void crossLink() throws DescriptorValidationException {
     }
 
     /** See {@link FileDescriptor#setProto}. */
-    private void setProto(final ServiceDescriptorProto proto) {
+    private void setProto(final ServiceDescriptorProto proto) throws DescriptorValidationException {
       this.proto = proto;
       this.options = null;
       this.features = resolveFeatures(proto.getOptions().getFeatures());
@@ -2655,7 +2667,7 @@ private MethodDescriptor(
     }
 
     /** See {@link FileDescriptor#resolveAllFeatures}. */
-    private void resolveAllFeatures() {
+    private void resolveAllFeatures() throws DescriptorValidationException {
       this.features = resolveFeatures(proto.getOptions().getFeatures());
     }
 
@@ -2682,7 +2694,7 @@ private void crossLink() throws DescriptorValidationException {
     }
 
     /** See {@link FileDescriptor#setProto}. */
-    private void setProto(final MethodDescriptorProto proto) {
+    private void setProto(final MethodDescriptorProto proto) throws DescriptorValidationException {
       this.proto = proto;
       this.options = null;
       this.features = resolveFeatures(proto.getOptions().getFeatures());
@@ -2723,7 +2735,7 @@ private GenericDescriptor() {}
 
     public abstract FileDescriptor getFile();
 
-    FeatureSet resolveFeatures(FeatureSet unresolvedFeatures) {
+    FeatureSet resolveFeatures(FeatureSet unresolvedFeatures) throws DescriptorValidationException {
       if (this.parent != null
           && unresolvedFeatures.equals(FeatureSet.getDefaultInstance())
           && !hasInferredLegacyProtoFeatures()) {
@@ -2738,6 +2750,7 @@ FeatureSet resolveFeatures(FeatureSet unresolvedFeatures) {
       }
       features.mergeFrom(inferLegacyProtoFeatures());
       features.mergeFrom(unresolvedFeatures);
+      validateFeatures(features.build());
       return internFeatures(features.build());
     }
 
@@ -2749,6 +2762,9 @@ boolean hasInferredLegacyProtoFeatures() {
       return false;
     }
 
+    void validateFeatures(FeatureSet features) throws DescriptorValidationException {
+    }
+
     GenericDescriptor parent;
     volatile FeatureSet features;
   }
@@ -3214,11 +3230,11 @@ boolean isSynthetic() {
     }
 
     /** See {@link FileDescriptor#resolveAllFeatures}. */
-    private void resolveAllFeatures() {
+    private void resolveAllFeatures() throws DescriptorValidationException {
       this.features = resolveFeatures(proto.getOptions().getFeatures());
     }
 
-    private void setProto(final OneofDescriptorProto proto) {
+    private void setProto(final OneofDescriptorProto proto) throws DescriptorValidationException {
       this.proto = proto;
       this.options = null;
       this.features = resolveFeatures(proto.getOptions().getFeatures());