diff --git a/config/src/test/java/org/springframework/security/SpringSecurityCoreVersionSerializableTests.java b/config/src/test/java/org/springframework/security/SpringSecurityCoreVersionSerializableTests.java
index 5072da9f5c4..4a6243d16e1 100644
--- a/config/src/test/java/org/springframework/security/SpringSecurityCoreVersionSerializableTests.java
+++ b/config/src/test/java/org/springframework/security/SpringSecurityCoreVersionSerializableTests.java
@@ -126,6 +126,8 @@
 import org.springframework.security.saml2.provider.service.authentication.TestSaml2Authentications;
 import org.springframework.security.saml2.provider.service.authentication.TestSaml2PostAuthenticationRequests;
 import org.springframework.security.saml2.provider.service.authentication.TestSaml2RedirectAuthenticationRequests;
+import org.springframework.security.saml2.provider.service.registration.RelyingPartyRegistration;
+import org.springframework.security.saml2.provider.service.registration.TestRelyingPartyRegistrations;
 import org.springframework.security.web.authentication.WebAuthenticationDetails;
 import org.springframework.security.web.authentication.preauth.PreAuthenticatedAuthenticationToken;
 import org.springframework.security.web.authentication.preauth.PreAuthenticatedCredentialsNotFoundException;
@@ -322,6 +324,7 @@ class SpringSecurityCoreVersionSerializableTests {
 				(r) -> TestSaml2PostAuthenticationRequests.create());
 		generatorByClassName.put(Saml2RedirectAuthenticationRequest.class,
 				(r) -> TestSaml2RedirectAuthenticationRequests.create());
+		generatorByClassName.put(RelyingPartyRegistration.class, (r) -> TestRelyingPartyRegistrations.full().build());
 
 		// web
 		generatorByClassName.put(AnonymousAuthenticationToken.class, (r) -> {
diff --git a/config/src/test/resources/serialized/6.5.x/org.springframework.security.saml2.core.Saml2X509Credential.serialized b/config/src/test/resources/serialized/6.5.x/org.springframework.security.saml2.core.Saml2X509Credential.serialized
new file mode 100644
index 00000000000..4da506d7ba6
Binary files /dev/null and b/config/src/test/resources/serialized/6.5.x/org.springframework.security.saml2.core.Saml2X509Credential.serialized differ
diff --git a/config/src/test/resources/serialized/6.5.x/org.springframework.security.saml2.provider.service.registration.RelyingPartyRegistration$AssertingPartyDetails.serialized b/config/src/test/resources/serialized/6.5.x/org.springframework.security.saml2.provider.service.registration.RelyingPartyRegistration$AssertingPartyDetails.serialized
new file mode 100644
index 00000000000..fc4e87f02b6
Binary files /dev/null and b/config/src/test/resources/serialized/6.5.x/org.springframework.security.saml2.provider.service.registration.RelyingPartyRegistration$AssertingPartyDetails.serialized differ
diff --git a/config/src/test/resources/serialized/6.5.x/org.springframework.security.saml2.provider.service.registration.RelyingPartyRegistration.serialized b/config/src/test/resources/serialized/6.5.x/org.springframework.security.saml2.provider.service.registration.RelyingPartyRegistration.serialized
new file mode 100644
index 00000000000..bcfee89198d
Binary files /dev/null and b/config/src/test/resources/serialized/6.5.x/org.springframework.security.saml2.provider.service.registration.RelyingPartyRegistration.serialized differ
diff --git a/saml2/saml2-service-provider/src/main/java/org/springframework/security/saml2/core/Saml2X509Credential.java b/saml2/saml2-service-provider/src/main/java/org/springframework/security/saml2/core/Saml2X509Credential.java
index a8126d26bde..18d7561348c 100644
--- a/saml2/saml2-service-provider/src/main/java/org/springframework/security/saml2/core/Saml2X509Credential.java
+++ b/saml2/saml2-service-provider/src/main/java/org/springframework/security/saml2/core/Saml2X509Credential.java
@@ -1,5 +1,5 @@
 /*
- * Copyright 2002-2020 the original author or authors.
+ * Copyright 2002-2024 the original author or authors.
  *
  * Licensed under the Apache License, Version 2.0 (the "License");
  * you may not use this file except in compliance with the License.
@@ -16,6 +16,7 @@
 
 package org.springframework.security.saml2.core;
 
+import java.io.Serializable;
 import java.security.PrivateKey;
 import java.security.cert.X509Certificate;
 import java.util.Arrays;
@@ -35,7 +36,9 @@
  * @author Josh Cummings
  * @since 5.4
  */
-public final class Saml2X509Credential {
+public final class Saml2X509Credential implements Serializable {
+
+	private static final long serialVersionUID = -1015853414272603517L;
 
 	private final PrivateKey privateKey;
 
diff --git a/saml2/saml2-service-provider/src/main/java/org/springframework/security/saml2/provider/service/registration/AssertingPartyMetadata.java b/saml2/saml2-service-provider/src/main/java/org/springframework/security/saml2/provider/service/registration/AssertingPartyMetadata.java
index c75de010d4e..985e5db51f1 100644
--- a/saml2/saml2-service-provider/src/main/java/org/springframework/security/saml2/provider/service/registration/AssertingPartyMetadata.java
+++ b/saml2/saml2-service-provider/src/main/java/org/springframework/security/saml2/provider/service/registration/AssertingPartyMetadata.java
@@ -16,6 +16,7 @@
 
 package org.springframework.security.saml2.provider.service.registration;
 
+import java.io.Serializable;
 import java.util.Collection;
 import java.util.List;
 import java.util.function.Consumer;
@@ -28,7 +29,7 @@
  * @author Josh Cummings
  * @since 6.4
  */
-public interface AssertingPartyMetadata {
+public interface AssertingPartyMetadata extends Serializable {
 
 	/**
 	 * Get the asserting party's <a href=
diff --git a/saml2/saml2-service-provider/src/main/java/org/springframework/security/saml2/provider/service/registration/RelyingPartyRegistration.java b/saml2/saml2-service-provider/src/main/java/org/springframework/security/saml2/provider/service/registration/RelyingPartyRegistration.java
index 9927c3a9c14..69f0c822190 100644
--- a/saml2/saml2-service-provider/src/main/java/org/springframework/security/saml2/provider/service/registration/RelyingPartyRegistration.java
+++ b/saml2/saml2-service-provider/src/main/java/org/springframework/security/saml2/provider/service/registration/RelyingPartyRegistration.java
@@ -1,5 +1,5 @@
 /*
- * Copyright 2002-2023 the original author or authors.
+ * Copyright 2002-2024 the original author or authors.
  *
  * Licensed under the Apache License, Version 2.0 (the "License");
  * you may not use this file except in compliance with the License.
@@ -16,6 +16,7 @@
 
 package org.springframework.security.saml2.provider.service.registration;
 
+import java.io.Serializable;
 import java.util.ArrayList;
 import java.util.Collection;
 import java.util.Collections;
@@ -66,7 +67,9 @@
  * @author Josh Cummings
  * @since 5.2
  */
-public class RelyingPartyRegistration {
+public class RelyingPartyRegistration implements Serializable {
+
+	private static final long serialVersionUID = -2718908121120942813L;
 
 	private final String registrationId;
 
@@ -456,6 +459,8 @@ public static Builder withRelyingPartyRegistration(RelyingPartyRegistration regi
 	 */
 	public static class AssertingPartyDetails implements AssertingPartyMetadata {
 
+		private static final long serialVersionUID = 8728930758311995475L;
+
 		private final String entityId;
 
 		private final boolean wantAuthnRequestsSigned;