diff --git a/lib/httparty.rb b/lib/httparty.rb
index 021c27a1..16ad5042 100644
--- a/lib/httparty.rb
+++ b/lib/httparty.rb
@@ -353,6 +353,11 @@ def pkcs12(p12_contents, password)
       default_options[:p12_password] = password
     end
 
+    # Allow using a full certificate chain (http.extra_chain_cert)
+    def extra_chain_cert(value = false)
+      default_options[:extra_chain_cert] = value
+    end
+
     # Override the way query strings are normalized.
     # Helpful for overriding the default rails normalization of Array queries.
     #
diff --git a/lib/httparty/connection_adapter.rb b/lib/httparty/connection_adapter.rb
index 262016fb..71aa7e5c 100644
--- a/lib/httparty/connection_adapter.rb
+++ b/lib/httparty/connection_adapter.rb
@@ -231,6 +231,12 @@ def attach_ssl_certificates(http, options)
         if options[:ssl_version] && http.respond_to?(:ssl_version=)
           http.ssl_version = options[:ssl_version]
         end
+
+        # Include full certificate chain
+        # Only Ruby 3.0+
+        if options[:extra_chain_cert] && options[:p12] && http.respond_to?(:extra_chain_cert=)
+          http.extra_chain_cert = [p12.certificate] + p12.ca_certs
+        end
       end
     end
   end
diff --git a/spec/httparty/connection_adapter_spec.rb b/spec/httparty/connection_adapter_spec.rb
index de386f87..02ce9ddf 100644
--- a/spec/httparty/connection_adapter_spec.rb
+++ b/spec/httparty/connection_adapter_spec.rb
@@ -628,6 +628,24 @@
               expect(subject.verify_mode).to eq(OpenSSL::SSL::VERIFY_NONE)
             end
           end
+
+          context "when using extra_chain_cert and p12" do
+            let(:options) { { p12: p12, p12_password: "password", extra_chain_cert: true } }
+
+            before { allow(pkcs12).to receive(:ca_certs).and_return([double("OpenSSL::X509::Certificate")]) }
+
+            it "does not set extra_chain_cert on unsupported ruby versions" do
+              if !(subject.respond_to?(:extra_chain_cert=))
+                expect(subject).to_not receive(:extra_chain_cert=)
+              end
+            end
+
+            it "sets extra_chain_cert on http object in Ruby 3.0+" do
+              if subject.respond_to?(:extra_chain_cert=)
+                expect(subject.extra_chain_cert).to eq([cert] + pkcs12.ca_certs)
+              end
+            end
+          end
         end
 
         context "when scheme is not https" do
diff --git a/spec/httparty_spec.rb b/spec/httparty_spec.rb
index b6055298..915ae9dc 100644
--- a/spec/httparty_spec.rb
+++ b/spec/httparty_spec.rb
@@ -35,6 +35,13 @@
     end
   end
 
+  describe "extra_chain_cert" do
+    it 'should set the extra_chain_cert option' do
+      @klass.extra_chain_cert true
+      expect(@klass.default_options[:extra_chain_cert]).to eq(true)
+    end
+  end
+
   describe 'ssl_version' do
     it 'should set the ssl_version content' do
       @klass.ssl_version :SSLv3