diff --git a/lib/protobuf/field/bytes_field.rb b/lib/protobuf/field/bytes_field.rb
index 81a3634d..b8d88078 100644
--- a/lib/protobuf/field/bytes_field.rb
+++ b/lib/protobuf/field/bytes_field.rb
@@ -59,7 +59,7 @@ def coerce!(value)
         end
       end
 
-      def json_encode(value)
+      def json_encode(value, options={})
         Base64.strict_encode64(value)
       end
     end
diff --git a/lib/protobuf/field/int64_field.rb b/lib/protobuf/field/int64_field.rb
index 3b338894..f2597b25 100644
--- a/lib/protobuf/field/int64_field.rb
+++ b/lib/protobuf/field/int64_field.rb
@@ -29,6 +29,13 @@ def acceptable?(val)
         return false
       end
 
+      def json_encode(value, options = {})
+        if options[:proto3]
+          value == 0 ? nil : value.to_s
+        else
+          value
+        end
+      end
     end
   end
 end
diff --git a/lib/protobuf/field/sint64_field.rb b/lib/protobuf/field/sint64_field.rb
index 2aba7dfa..0c1c0856 100644
--- a/lib/protobuf/field/sint64_field.rb
+++ b/lib/protobuf/field/sint64_field.rb
@@ -16,6 +16,13 @@ def self.min
         INT64_MIN
       end
 
+      def json_encode(value, options = {})
+        if options[:proto3]
+          value == 0 ? nil : value.to_s
+        else
+          value
+        end
+      end
     end
   end
 end
diff --git a/lib/protobuf/field/string_field.rb b/lib/protobuf/field/string_field.rb
index 6c9c278f..551bdd23 100644
--- a/lib/protobuf/field/string_field.rb
+++ b/lib/protobuf/field/string_field.rb
@@ -43,7 +43,7 @@ def encode(value)
         "#{::Protobuf::Field::VarintField.encode(value_to_encode.bytesize)}#{value_to_encode}"
       end
 
-      def json_encode(value)
+      def json_encode(value, options={})
         value
       end
     end
diff --git a/lib/protobuf/field/uint64_field.rb b/lib/protobuf/field/uint64_field.rb
index 8a060f14..df041fc5 100644
--- a/lib/protobuf/field/uint64_field.rb
+++ b/lib/protobuf/field/uint64_field.rb
@@ -16,6 +16,13 @@ def self.min
         0
       end
 
+      def json_encode(value, options = {})
+        if options[:proto3]
+          value == 0 ? nil : value.to_s
+        else
+          value
+        end
+      end
     end
   end
 end
diff --git a/lib/protobuf/message.rb b/lib/protobuf/message.rb
index 06b26b94..87e15566 100644
--- a/lib/protobuf/message.rb
+++ b/lib/protobuf/message.rb
@@ -142,7 +142,7 @@ def to_json(options = {})
     def to_json_hash(options = {})
       result = {}
 
-      lower_camel_case = options[:lower_camel_case]
+      proto3 = options[:proto3] || options[:lower_camel_case]
 
       @values.each_key do |field_name|
         value = self[field_name]
@@ -153,13 +153,17 @@ def to_json_hash(options = {})
         hashed_value = if value.respond_to?(:to_json_hash_value)
                          value.to_json_hash_value(options)
                        elsif field.respond_to?(:json_encode)
-                         field.json_encode(value)
+                         field.json_encode(value, options)
                        else
                          value
                        end
 
-        key = lower_camel_case ? field.name.to_s.camelize(:lower).to_sym : field.name
-        result[key] = hashed_value
+        if proto3 && (hashed_value.nil? || value == field.class.default)
+          result.delete(field.name)
+        else
+          key = proto3 ? field.name.to_s.camelize(:lower).to_sym : field.name
+          result[key] = hashed_value
+        end
       end
 
       result
diff --git a/spec/lib/protobuf/field/fixed64_field_spec.rb b/spec/lib/protobuf/field/fixed64_field_spec.rb
index d7feb120..00ad743a 100644
--- a/spec/lib/protobuf/field/fixed64_field_spec.rb
+++ b/spec/lib/protobuf/field/fixed64_field_spec.rb
@@ -4,4 +4,30 @@
 
   it_behaves_like :packable_field, described_class
 
+  let(:message) do
+    Class.new(::Protobuf::Message) do
+      optional :fixed64, :some_field, 1
+    end
+  end
+
+  # https://developers.google.com/protocol-buffers/docs/proto3#json
+  describe '.{to_json, from_json}' do
+    it 'serialises 0' do
+      instance = message.new(some_field: 0)
+      expect(instance.to_json(proto3: true)).to eq('{}')
+      expect(instance.to_json).to eq('{"some_field":0}')
+    end
+
+    it 'serialises max value' do
+      instance = message.new(some_field: described_class.max)
+      expect(instance.to_json(proto3: true)).to eq('{"someField":"18446744073709551615"}')
+      expect(instance.to_json).to eq('{"some_field":18446744073709551615}')
+    end
+
+    it 'serialises min value' do
+      instance = message.new(some_field: described_class.min)
+      expect(instance.to_json(proto3: true)).to eq('{}')
+      expect(instance.to_json).to eq('{"some_field":0}')
+    end
+  end
 end
diff --git a/spec/lib/protobuf/field/int64_field_spec.rb b/spec/lib/protobuf/field/int64_field_spec.rb
index 1bbe7c04..d0c77d34 100644
--- a/spec/lib/protobuf/field/int64_field_spec.rb
+++ b/spec/lib/protobuf/field/int64_field_spec.rb
@@ -4,4 +4,30 @@
 
   it_behaves_like :packable_field, described_class
 
+  let(:message) do
+    Class.new(::Protobuf::Message) do
+      optional :int64, :some_field, 1
+    end
+  end
+
+  # https://developers.google.com/protocol-buffers/docs/proto3#json
+  describe '.{to_json, from_json}' do
+    it 'serialises 0' do
+      instance = message.new(some_field: 0)
+      expect(instance.to_json(proto3: true)).to eq('{}')
+      expect(instance.to_json).to eq('{"some_field":0}')
+    end
+
+    it 'serialises max value' do
+      instance = message.new(some_field: described_class.max)
+      expect(instance.to_json(proto3: true)).to eq('{"someField":"9223372036854775807"}')
+      expect(instance.to_json).to eq('{"some_field":9223372036854775807}')
+    end
+
+    it 'serialises min value' do
+      instance = message.new(some_field: described_class.min)
+      expect(instance.to_json(proto3: true)).to eq('{"someField":"-9223372036854775808"}')
+      expect(instance.to_json).to eq('{"some_field":-9223372036854775808}')
+    end
+  end
 end
diff --git a/spec/lib/protobuf/field/sfixed64_field_spec.rb b/spec/lib/protobuf/field/sfixed64_field_spec.rb
index f380ed5d..7988f45f 100644
--- a/spec/lib/protobuf/field/sfixed64_field_spec.rb
+++ b/spec/lib/protobuf/field/sfixed64_field_spec.rb
@@ -6,4 +6,30 @@
     let(:value) { [-1, 0, 1] }
   end
 
+  let(:message) do
+    Class.new(::Protobuf::Message) do
+      optional :sfixed64, :some_field, 1
+    end
+  end
+
+  # https://developers.google.com/protocol-buffers/docs/proto3#json
+  describe '.{to_json, from_json}' do
+    it 'serialises 0' do
+      instance = message.new(some_field: 0)
+      expect(instance.to_json(proto3: true)).to eq('{}')
+      expect(instance.to_json).to eq('{"some_field":0}')
+    end
+
+    it 'serialises max value' do
+      instance = message.new(some_field: described_class.max)
+      expect(instance.to_json(proto3: true)).to eq('{"someField":"9223372036854775807"}')
+      expect(instance.to_json).to eq('{"some_field":9223372036854775807}')
+    end
+
+    it 'serialises min value as string' do
+      instance = message.new(some_field: described_class.min)
+      expect(instance.to_json(proto3: true)).to eq('{"someField":"-9223372036854775808"}')
+      expect(instance.to_json).to eq('{"some_field":-9223372036854775808}')
+    end
+  end
 end
diff --git a/spec/lib/protobuf/field/sint64_field_spec.rb b/spec/lib/protobuf/field/sint64_field_spec.rb
index 84ca7304..e6fc05ff 100644
--- a/spec/lib/protobuf/field/sint64_field_spec.rb
+++ b/spec/lib/protobuf/field/sint64_field_spec.rb
@@ -6,4 +6,30 @@
     let(:value) { [-1, 0, 1] }
   end
 
+  let(:message) do
+    Class.new(::Protobuf::Message) do
+      optional :sint64, :some_field, 1
+    end
+  end
+
+  # https://developers.google.com/protocol-buffers/docs/proto3#json
+  describe '.{to_json, from_json}' do
+    it 'serialises 0' do
+      instance = message.new(some_field: 0)
+      expect(instance.to_json(proto3: true)).to eq('{}')
+      expect(instance.to_json).to eq('{"some_field":0}')
+    end
+
+    it 'serialises max value as string' do
+      instance = message.new(some_field: described_class.max)
+      expect(instance.to_json(proto3: true)).to eq('{"someField":"9223372036854775807"}')
+      expect(instance.to_json).to eq('{"some_field":9223372036854775807}')
+    end
+
+    it 'serialises min value as string' do
+      instance = message.new(some_field: described_class.min)
+      expect(instance.to_json(proto3: true)).to eq('{"someField":"-9223372036854775808"}')
+      expect(instance.to_json).to eq('{"some_field":-9223372036854775808}')
+    end
+  end
 end
diff --git a/spec/lib/protobuf/field/uint64_field_spec.rb b/spec/lib/protobuf/field/uint64_field_spec.rb
index 61b8d1b9..90bc0306 100644
--- a/spec/lib/protobuf/field/uint64_field_spec.rb
+++ b/spec/lib/protobuf/field/uint64_field_spec.rb
@@ -4,4 +4,30 @@
 
   it_behaves_like :packable_field, described_class
 
+  let(:message) do
+    Class.new(::Protobuf::Message) do
+      optional :uint64, :some_field, 1
+    end
+  end
+
+  # https://developers.google.com/protocol-buffers/docs/proto3#json
+  describe '.{to_json, from_json}' do
+    it 'serialises 0' do
+      instance = message.new(some_field: 0)
+      expect(instance.to_json(proto3: true)).to eq('{}')
+      expect(instance.to_json).to eq('{"some_field":0}')
+    end
+
+    it 'serialises max value' do
+      instance = message.new(some_field: described_class.max)
+      expect(instance.to_json(proto3: true)).to eq('{"someField":"18446744073709551615"}')
+      expect(instance.to_json).to eq('{"some_field":18446744073709551615}')
+    end
+
+    it 'serialises min value' do
+      instance = message.new(some_field: described_class.min)
+      expect(instance.to_json(proto3: true)).to eq('{}')
+      expect(instance.to_json).to eq('{"some_field":0}')
+    end
+  end
 end
diff --git a/spec/lib/protobuf/message_spec.rb b/spec/lib/protobuf/message_spec.rb
index 13110bc9..c6e9720d 100644
--- a/spec/lib/protobuf/message_spec.rb
+++ b/spec/lib/protobuf/message_spec.rb
@@ -438,14 +438,14 @@
       specify { expect(subject.to_json).to eq '{"widget_bytes":["Bo0xSFAXOmI="]}' }
     end
 
-    context 'using lower camel case field names' do
+    context 'using proto3 produces lower case field names' do
       let(:bytes) { "\x06\x8D1HP\x17:b" }
 
       subject do
         ::Test::ResourceFindRequest.new(:widget_bytes => [bytes])
       end
 
-      specify { expect(subject.to_json(:lower_camel_case => true)).to eq '{"widgetBytes":["Bo0xSFAXOmI="]}' }
+      specify { expect(subject.to_json(:proto3 => true)).to eq '{"widgetBytes":["Bo0xSFAXOmI="]}' }
     end
   end