diff --git a/CHANGELOG.md b/CHANGELOG.md
index c651ba5..0dfe8fa 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -1,5 +1,10 @@
 # Changelog
 
+## Unreleased
+
+* [FIXED] Use `MultiJSON.generate` and `MultiJSON.parse` to avoid multi_json 1.21+ deprecation warnings.
+* [CHANGED] Require multi_json 1.21 or later within the 1.x series.
+
 ## 2.1.1
 
 * [FIXED] Fix MultiJson deprecation warnings (encode/decode → dump/load)
diff --git a/lib/pusher/channel.rb b/lib/pusher/channel.rb
index 57e88fc..4337041 100644
--- a/lib/pusher/channel.rb
+++ b/lib/pusher/channel.rb
@@ -156,7 +156,7 @@ def authentication_string(socket_id, custom_string = nil)
     # @private Custom data is sent to server as JSON-encoded string
     #
     def authenticate(socket_id, custom_data = nil)
-      custom_data = MultiJson.dump(custom_data) if custom_data
+      custom_data = MultiJSON.generate(custom_data) if custom_data
       auth = authentication_string(socket_id, custom_data)
       r = {:auth => auth}
       r[:channel_data] = custom_data if custom_data
diff --git a/lib/pusher/client.rb b/lib/pusher/client.rb
index 00194b2..2bab49e 100644
--- a/lib/pusher/client.rb
+++ b/lib/pusher/client.rb
@@ -374,7 +374,7 @@ def authenticate(channel_name, socket_id, custom_data = nil)
     def authenticate_user(socket_id, user_data)
       validate_user_data(user_data)
 
-      custom_data = MultiJson.dump(user_data)
+      custom_data = MultiJSON.generate(user_data)
       auth = authentication_string(socket_id, custom_data)
 
       { auth:, user_data: custom_data }
@@ -461,7 +461,7 @@ def trigger_batch_params(events)
     # JSON-encode the data if it's not a string
     def encode_data(data)
       return data if data.is_a? String
-      MultiJson.dump(data)
+      MultiJSON.generate(data)
     end
 
     # Encrypts a message with a key derived from the master key and channel
@@ -480,7 +480,7 @@ def encrypt(channel_name, encoded_data)
       nonce = RbNaCl::Random.random_bytes(secret_box.nonce_bytes)
       ciphertext = secret_box.encrypt(nonce, encoded_data)
 
-      MultiJson.dump({
+      MultiJSON.generate({
         "nonce" => Base64::strict_encode64(nonce),
         "ciphertext" => Base64::strict_encode64(ciphertext),
       })
diff --git a/lib/pusher/request.rb b/lib/pusher/request.rb
index 4edf9ff..6dbe288 100644
--- a/lib/pusher/request.rb
+++ b/lib/pusher/request.rb
@@ -86,9 +86,9 @@ def send_async
     def handle_response(status_code, body)
       case status_code
       when 200
-        return symbolize_first_level(MultiJson.load(body))
+        return symbolize_first_level(MultiJSON.parse(body))
       when 202
-        return body.empty? ? true : symbolize_first_level(MultiJson.load(body))
+        return body.empty? ? true : symbolize_first_level(MultiJSON.parse(body))
       when 400
         raise Error, "Bad request: #{body}"
       when 401
diff --git a/lib/pusher/resource.rb b/lib/pusher/resource.rb
index 8a0cf2b..30ea174 100644
--- a/lib/pusher/resource.rb
+++ b/lib/pusher/resource.rb
@@ -14,12 +14,12 @@ def get_async(params)
     end
 
     def post(params)
-      body = MultiJson.dump(params)
+      body = MultiJSON.generate(params)
       create_request(:post, {}, body).send_sync
     end
 
     def post_async(params)
-      body = MultiJson.dump(params)
+      body = MultiJSON.generate(params)
       create_request(:post, {}, body).send_async
     end
 
diff --git a/lib/pusher/webhook.rb b/lib/pusher/webhook.rb
index 71714ba..d6e5205 100644
--- a/lib/pusher/webhook.rb
+++ b/lib/pusher/webhook.rb
@@ -88,7 +88,7 @@ def data
       @data ||= begin
         case @content_type
         when 'application/json'
-          MultiJson.load(@body)
+          MultiJSON.parse(@body)
         else
           raise "Unknown Content-Type (#{@content_type})"
         end
diff --git a/pusher.gemspec b/pusher.gemspec
index d4cc697..42a462f 100644
--- a/pusher.gemspec
+++ b/pusher.gemspec
@@ -15,7 +15,7 @@ Gem::Specification.new do |s|
 
   s.required_ruby_version = ">= 3.1"
 
-  s.add_dependency "multi_json", "~> 1.15"
+  s.add_dependency "multi_json", "~> 1.21"
   s.add_dependency 'pusher-signature', "~> 0.1.8"
   s.add_dependency "httpclient", "~> 2.8"
   s.add_dependency "jruby-openssl" if defined?(JRUBY_VERSION)
diff --git a/spec/channel_spec.rb b/spec/channel_spec.rb
index aef45d1..d72c071 100644
--- a/spec/channel_spec.rb
+++ b/spec/channel_spec.rb
@@ -133,7 +133,7 @@ def authentication_string(*data)
     end
 
     it 'should return a hash with signature including custom data and data as json string' do
-      allow(MultiJson).to receive(:dump).with(@custom_data).and_return 'a json string'
+      allow(MultiJSON).to receive(:generate).with(@custom_data).and_return 'a json string'
 
       response = @channel.authenticate('1.1', @custom_data)
 
diff --git a/spec/client_spec.rb b/spec/client_spec.rb
index 96f41b2..8f4b6b3 100644
--- a/spec/client_spec.rb
+++ b/spec/client_spec.rb
@@ -235,7 +235,7 @@
           api_path = %r{/apps/20/channels}
           stub_request(:get, api_path).to_return({
             :status => 200,
-            :body => MultiJson.dump('channels' => {
+            :body => MultiJSON.generate('channels' => {
               "channel1" => {},
               "channel2" => {}
             })
@@ -254,7 +254,7 @@
           api_path = %r{/apps/20/channels/mychannel}
           stub_request(:get, api_path).to_return({
             :status => 200,
-            :body => MultiJson.dump({
+            :body => MultiJSON.generate({
               'occupied' => false,
             })
           })
@@ -288,7 +288,7 @@
           stub_request(:get, api_path)
             .to_return({ :status => 500, :body => "Server error" })
             .then
-            .to_return({ :status => 200, :body => MultiJson.dump({ 'occupied' => false }) })
+            .to_return({ :status => 200, :body => MultiJSON.generate({ 'occupied' => false }) })
 
           expect { @client.channel_info('mychannel') }.to raise_error(Pusher::Error)
           expect(@client.channel_info('mychannel')).to eq({ :occupied => false })
@@ -298,7 +298,7 @@
           api_path = %r{/apps/20/channels/mychannel}
           stub_request(:get, api_path).to_return({
             :status => 200,
-            :body => MultiJson.dump({ 'occupied' => false })
+            :body => MultiJSON.generate({ 'occupied' => false })
           })
 
           http_client = @client.sync_http_client
@@ -313,7 +313,7 @@
           api_path = %r{/apps/20/channels/mychannel/users}
           stub_request(:get, api_path).to_return({
             :status => 200,
-            :body => MultiJson.dump({
+            :body => MultiJSON.generate({
               'users' => [{ 'id' => 1 }]
             })
           })
@@ -329,7 +329,7 @@
         end
 
         it 'should return a hash with signature including custom data and data as json string' do
-          allow(MultiJson).to receive(:dump).with(@custom_data).and_return 'a json string'
+          allow(MultiJSON).to receive(:generate).with(@custom_data).and_return 'a json string'
 
           response = @client.authenticate('test_channel', '1.1', @custom_data)
 
@@ -340,7 +340,7 @@
         end
 
         it 'should include a shared_secret if the private-encrypted channel' do
-          allow(MultiJson).to receive(:dump).with(@custom_data).and_return 'a json string'
+          allow(MultiJSON).to receive(:generate).with(@custom_data).and_return 'a json string'
           @client.instance_variable_set(:@encryption_master_key, '3W1pfB/Etr+ZIlfMWwZP3gz8jEeCt4s2pe6Vpr+2c3M=')
 
           response = @client.authenticate('private-encrypted-test_channel', '1.1', @custom_data)
@@ -360,7 +360,7 @@
         end
 
         it 'should return a hash with signature including custom data and data as json string' do
-          allow(MultiJson).to receive(:dump).with(@user_data).and_return 'a json string'
+          allow(MultiJSON).to receive(:generate).with(@user_data).and_return 'a json string'
 
           response = @client.authenticate_user('1.1', @user_data)
 
@@ -377,7 +377,7 @@
           @api_path = %r{/apps/20/events}
           stub_request(:post, @api_path).to_return({
             :status => 200,
-            :body => MultiJson.dump({})
+            :body => MultiJSON.generate({})
           })
         end
 
@@ -399,7 +399,7 @@
             :socket_id => "12.34"
           })
           expect(WebMock).to have_requested(:post, @api_path).with { |req|
-            parsed = MultiJson.load(req.body)
+            parsed = MultiJSON.parse(req.body)
             expect(parsed["name"]).to eq('event')
             expect(parsed["channels"]).to eq(["mychannel", "c2"])
             expect(parsed["socket_id"]).to eq('12.34')
@@ -409,14 +409,14 @@
         it "should convert non string data to JSON before posting" do
           @client.trigger(['mychannel'], 'event', {'some' => 'data'})
           expect(WebMock).to have_requested(:post, @api_path).with { |req|
-            expect(MultiJson.load(req.body)["data"]).to eq('{"some":"data"}')
+            expect(MultiJSON.parse(req.body)["data"]).to eq('{"some":"data"}')
           }
         end
 
         it "should accept a single channel as well as an array" do
           @client.trigger('mychannel', 'event', {'some' => 'data'})
           expect(WebMock).to have_requested(:post, @api_path).with { |req|
-            expect(MultiJson.load(req.body)["channels"]).to eq(['mychannel'])
+            expect(MultiJSON.parse(req.body)["channels"]).to eq(['mychannel'])
           }
         end
 
@@ -427,7 +427,7 @@
               @client.trigger('mychannel', 'event', {'some' => 'data'})
             }.to raise_error(Pusher::ConfigurationError)
             expect(WebMock).not_to have_requested(:post, @api_path).with { |req|
-              expect(MultiJson.load(req.body)["channels"]).to eq(['mychannel'])
+              expect(MultiJSON.parse(req.body)["channels"]).to eq(['mychannel'])
             }
           end
         end
@@ -459,13 +459,13 @@
           )
 
           expect(WebMock).to have_requested(:post, @api_path).with { |req|
-            data = MultiJson.load(MultiJson.load(req.body)["data"])
+            data = MultiJSON.parse(MultiJSON.parse(req.body)["data"])
 
             key = RbNaCl::Hash.sha256(
               'private-encrypted-channel' + encryption_master_key
             )
 
-            expect(MultiJson.load(RbNaCl::SecretBox.new(key).decrypt(
+            expect(MultiJSON.parse(RbNaCl::SecretBox.new(key).decrypt(
               Base64.strict_decode64(data["nonce"]),
               Base64.strict_decode64(data["ciphertext"]),
             ))).to eq({ 'some' => 'data' })
@@ -478,7 +478,7 @@
           @api_path = %r{/apps/20/batch_events}
           stub_request(:post, @api_path).to_return({
             :status => 200,
-            :body => MultiJson.dump({})
+            :body => MultiJSON.generate({})
           })
         end
 
@@ -493,7 +493,7 @@
             {channel: 'mychannel', name: 'event', data: 'already encoded'},
           )
           expect(WebMock).to have_requested(:post, @api_path).with { |req|
-            parsed = MultiJson.load(req.body)
+            parsed = MultiJSON.parse(req.body)
             expect(parsed).to eq(
               "batch" => [
                 { "channel" => "mychannel", "name" => "event", "data" => "{\"some\":\"data\"}"},
@@ -529,19 +529,19 @@
           )
 
           expect(WebMock).to have_requested(:post, @api_path).with { |req|
-            batch = MultiJson.load(req.body)["batch"]
+            batch = MultiJSON.parse(req.body)["batch"]
             expect(batch.length).to eq(2)
 
             expect(batch[0]["channel"]).to eq("private-encrypted-channel")
             expect(batch[0]["name"]).to eq("event")
 
-            data = MultiJson.load(batch[0]["data"])
+            data = MultiJSON.parse(batch[0]["data"])
 
             key = RbNaCl::Hash.sha256(
               'private-encrypted-channel' + encryption_master_key
             )
 
-            expect(MultiJson.load(RbNaCl::SecretBox.new(key).decrypt(
+            expect(MultiJSON.parse(RbNaCl::SecretBox.new(key).decrypt(
               Base64.strict_decode64(data["nonce"]),
               Base64.strict_decode64(data["ciphertext"]),
             ))).to eq({ 'some' => 'data' })
@@ -558,7 +558,7 @@
           @api_path = %r{/apps/20/events}
           stub_request(:post, @api_path).to_return({
             :status => 200,
-            :body => MultiJson.dump({})
+            :body => MultiJSON.generate({})
           })
         end
 
@@ -577,7 +577,7 @@
               :socket_id => "12.34"
             }).callback {
               expect(WebMock).to have_requested(:post, @api_path).with { |req|
-                expect(MultiJson.load(req.body)["socket_id"]).to eq('12.34')
+                expect(MultiJSON.parse(req.body)["socket_id"]).to eq('12.34')
               }
               EM.stop
             }
@@ -588,7 +588,7 @@
           EM.run {
             @client.trigger_async('mychannel', 'event', {'some' => 'data'}).callback {
               expect(WebMock).to have_requested(:post, @api_path).with { |req|
-                expect(MultiJson.load(req.body)["data"]).to eq('{"some":"data"}')
+                expect(MultiJSON.parse(req.body)["data"]).to eq('{"some":"data"}')
               }
               EM.stop
             }
@@ -620,7 +620,7 @@
           it "should format the respose hash with symbols at first level" do
             stub_request(verb, @url_regexp).to_return({
               :status => 200,
-              :body => MultiJson.dump({'something' => {'a' => 'hash'}})
+              :body => MultiJSON.generate({'something' => {'a' => 'hash'}})
             })
             expect(call_api).to eq({
               :something => {'a' => 'hash'}
@@ -751,7 +751,7 @@
               EM.run {
                 stub_request(verb, @url_regexp).to_return({
                   :status => 200,
-                  :body => MultiJson.dump({'something' => {'a' => 'hash'}})
+                  :body => MultiJSON.generate({'something' => {'a' => 'hash'}})
                 })
                 call_api.callback { |response|
                   expect(response).to eq({
diff --git a/spec/web_hook_spec.rb b/spec/web_hook_spec.rb
index 10118d8..1a3fdb3 100644
--- a/spec/web_hook_spec.rb
+++ b/spec/web_hook_spec.rb
@@ -19,7 +19,7 @@
         'HTTP_X_PUSHER_KEY' => '1234',
         'HTTP_X_PUSHER_SIGNATURE' => 'asdf',
         'CONTENT_TYPE' => 'application/json',
-        'rack.input' => StringIO.new(MultiJson.dump(@hook_data))
+        'rack.input' => StringIO.new(MultiJSON.generate(@hook_data))
       })
       wh = Pusher::WebHook.new(request)
       expect(wh.key).to eq('1234')
@@ -32,7 +32,7 @@
         :key => '1234',
         :signature => 'asdf',
         :content_type => 'application/json',
-        :body => MultiJson.dump(@hook_data),
+        :body => MultiJSON.generate(@hook_data),
       }
       wh = Pusher::WebHook.new(request)
       expect(wh.key).to eq('1234')
@@ -43,7 +43,7 @@
 
   describe "after initialization" do
     before :each do
-      @body = MultiJson.dump(@hook_data)
+      @body = MultiJSON.generate(@hook_data)
       request = {
         :key => '1234',
         :signature => hmac('asdf', @body),