diff --git a/src/google/protobuf/reflection_internal.h b/src/google/protobuf/reflection_internal.h
index ff62d58..b3cf659 100644
--- a/src/google/protobuf/reflection_internal.h
+++ b/src/google/protobuf/reflection_internal.h
@@ -203,7 +203,7 @@
  public:
   MapFieldAccessor() {}
   virtual ~MapFieldAccessor() {}
-  virtual bool IsEmpty(const Field* data) const {
+  bool IsEmpty(const Field* data) const override {
     return GetRepeatedField(data)->empty();
   }
   int Size(const Field* data) const override {
diff --git a/src/google/protobuf/util/internal/default_value_objectwriter.h b/src/google/protobuf/util/internal/default_value_objectwriter.h
index 7a8863c..89636dc 100644
--- a/src/google/protobuf/util/internal/default_value_objectwriter.h
+++ b/src/google/protobuf/util/internal/default_value_objectwriter.h
@@ -119,7 +119,7 @@
   DefaultValueObjectWriter* RenderBytes(StringPiece name,
                                         StringPiece value) override;
 
-  virtual DefaultValueObjectWriter* RenderNull(StringPiece name);
+  DefaultValueObjectWriter* RenderNull(StringPiece name) override;
 
   // Register the callback for scrubbing of fields. Owership of
   // field_scrub_callback pointer is also transferred to this class
diff --git a/src/google/protobuf/util/internal/json_objectwriter.h b/src/google/protobuf/util/internal/json_objectwriter.h
index ebfc7fb..2e19c9b 100644
--- a/src/google/protobuf/util/internal/json_objectwriter.h
+++ b/src/google/protobuf/util/internal/json_objectwriter.h
@@ -95,21 +95,20 @@
   virtual ~JsonObjectWriter();
 
   // ObjectWriter methods.
-  virtual JsonObjectWriter* StartObject(StringPiece name);
-  virtual JsonObjectWriter* EndObject();
-  virtual JsonObjectWriter* StartList(StringPiece name);
-  virtual JsonObjectWriter* EndList();
-  virtual JsonObjectWriter* RenderBool(StringPiece name, bool value);
-  virtual JsonObjectWriter* RenderInt32(StringPiece name, int32 value);
-  virtual JsonObjectWriter* RenderUint32(StringPiece name, uint32 value);
-  virtual JsonObjectWriter* RenderInt64(StringPiece name, int64 value);
-  virtual JsonObjectWriter* RenderUint64(StringPiece name, uint64 value);
-  virtual JsonObjectWriter* RenderDouble(StringPiece name, double value);
-  virtual JsonObjectWriter* RenderFloat(StringPiece name, float value);
-  virtual JsonObjectWriter* RenderString(StringPiece name,
-                                         StringPiece value);
-  virtual JsonObjectWriter* RenderBytes(StringPiece name, StringPiece value);
-  virtual JsonObjectWriter* RenderNull(StringPiece name);
+  JsonObjectWriter* StartObject(StringPiece name) override;
+  JsonObjectWriter* EndObject() override;
+  JsonObjectWriter* StartList(StringPiece name) override;
+  JsonObjectWriter* EndList() override;
+  JsonObjectWriter* RenderBool(StringPiece name, bool value) override;
+  JsonObjectWriter* RenderInt32(StringPiece name, int32 value) override;
+  JsonObjectWriter* RenderUint32(StringPiece name, uint32 value) override;
+  JsonObjectWriter* RenderInt64(StringPiece name, int64 value) override;
+  JsonObjectWriter* RenderUint64(StringPiece name, uint64 value) override;
+  JsonObjectWriter* RenderDouble(StringPiece name, double value) override;
+  JsonObjectWriter* RenderFloat(StringPiece name, float value) override;
+  JsonObjectWriter* RenderString(StringPiece name, StringPiece value) override;
+  JsonObjectWriter* RenderBytes(StringPiece name, StringPiece value) override;
+  JsonObjectWriter* RenderNull(StringPiece name) override;
   virtual JsonObjectWriter* RenderNullAsEmpty(StringPiece name);
 
   void set_use_websafe_base64_for_bytes(bool value) {
diff --git a/src/google/protobuf/util/json_util.cc b/src/google/protobuf/util/json_util.cc
index 0d2173c..8c0b4eb 100644
--- a/src/google/protobuf/util/json_util.cc
+++ b/src/google/protobuf/util/json_util.cc
@@ -129,9 +129,9 @@
 
   util::Status GetStatus() { return status_; }
 
-  virtual void InvalidName(const converter::LocationTrackerInterface& loc,
-                           StringPiece unknown_name,
-                           StringPiece message) {
+  void InvalidName(const converter::LocationTrackerInterface& loc,
+                   StringPiece unknown_name,
+                   StringPiece message) override {
     string loc_string = GetLocString(loc);
     if (!loc_string.empty()) {
       loc_string.append(" ");
@@ -141,17 +141,17 @@
                        StrCat(loc_string, unknown_name, ": ", message));
   }
 
-  virtual void InvalidValue(const converter::LocationTrackerInterface& loc,
-                            StringPiece type_name,
-                            StringPiece value) {
+  void InvalidValue(const converter::LocationTrackerInterface& loc,
+                    StringPiece type_name,
+                    StringPiece value) override {
     status_ = util::Status(
         util::error::INVALID_ARGUMENT,
         StrCat(GetLocString(loc), ": invalid value ", string(value),
                      " for type ", string(type_name)));
   }
 
-  virtual void MissingField(const converter::LocationTrackerInterface& loc,
-                            StringPiece missing_name) {
+  void MissingField(const converter::LocationTrackerInterface& loc,
+                    StringPiece missing_name) override {
     status_ = util::Status(util::error::INVALID_ARGUMENT,
                              StrCat(GetLocString(loc), ": missing field ",
                                           string(missing_name)));