diff --git a/core/src/main/java/org/springframework/security/jackson/CoreJacksonModule.java b/core/src/main/java/org/springframework/security/jackson/CoreJacksonModule.java
index 0d633f4c2de..60247c7a076 100644
--- a/core/src/main/java/org/springframework/security/jackson/CoreJacksonModule.java
+++ b/core/src/main/java/org/springframework/security/jackson/CoreJacksonModule.java
@@ -94,7 +94,13 @@ public void configurePolymorphicTypeValidator(BasicPolymorphicTypeValidator.Buil
 			.allowIfSubType("java.util.Collections$SingletonList")
 			.allowIfSubType("java.util.TreeMap")
 			.allowIfSubType("java.util.HashSet")
-			.allowIfSubType("java.util.LinkedHashSet");
+			.allowIfSubType("java.util.LinkedHashSet")
+			.allowIfSubType("java.util.ImmutableCollections$List12")
+			.allowIfSubType("java.util.ImmutableCollections$ListN")
+			.allowIfSubType("java.util.ImmutableCollections$Set12")
+			.allowIfSubType("java.util.ImmutableCollections$SetN")
+			.allowIfSubType("java.util.ImmutableCollections$Map1")
+			.allowIfSubType("java.util.ImmutableCollections$MapN");
 	}
 
 	@Override
diff --git a/core/src/test/java/org/springframework/security/jackson/ImmutableCollectionsTests.java b/core/src/test/java/org/springframework/security/jackson/ImmutableCollectionsTests.java
new file mode 100644
index 00000000000..fc4e3b874d5
--- /dev/null
+++ b/core/src/test/java/org/springframework/security/jackson/ImmutableCollectionsTests.java
@@ -0,0 +1,89 @@
+/*
+ * Copyright 2004-present 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.
+ * You may obtain a copy of the License at
+ *
+ *      https://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package org.springframework.security.jackson;
+
+import java.util.HashMap;
+import java.util.List;
+import java.util.Map;
+import java.util.Set;
+import java.util.stream.Stream;
+
+import org.junit.jupiter.api.Test;
+import tools.jackson.core.type.TypeReference;
+
+import static org.assertj.core.api.Assertions.assertThat;
+
+/**
+ * Tests that the JDK immutable collections created by {@code List.of}, {@code Set.of},
+ * {@code Map.of} and {@code Stream.toList()} can be serialized and deserialized.
+ *
+ * @author Rajesh Vasa
+ */
+class ImmutableCollectionsTests extends AbstractMixinTests {
+
+	private static final TypeReference<Map<String, Object>> MAP_TYPE = new TypeReference<>() {
+	};
+
+	@Test
+	void listOfOneElementWhenRoundTripThenDeserialized() throws Exception {
+		assertRoundTrip(List.of("a"));
+	}
+
+	@Test
+	void listOfManyElementsWhenRoundTripThenDeserialized() throws Exception {
+		assertRoundTrip(List.of("a", "b", "c"));
+	}
+
+	@Test
+	void emptyListOfWhenRoundTripThenDeserialized() throws Exception {
+		assertRoundTrip(List.of());
+	}
+
+	@Test
+	void streamToListWhenRoundTripThenDeserialized() throws Exception {
+		assertRoundTrip(Stream.of("ROLE_USER", "ROLE_ADMIN").toList());
+	}
+
+	@Test
+	void setOfOneElementWhenRoundTripThenDeserialized() throws Exception {
+		assertRoundTrip(Set.of("a"));
+	}
+
+	@Test
+	void setOfManyElementsWhenRoundTripThenDeserialized() throws Exception {
+		assertRoundTrip(Set.of("a", "b", "c"));
+	}
+
+	@Test
+	void mapOfOneEntryWhenRoundTripThenDeserialized() throws Exception {
+		assertRoundTrip(Map.of("k", "v"));
+	}
+
+	@Test
+	void mapOfManyEntriesWhenRoundTripThenDeserialized() throws Exception {
+		assertRoundTrip(Map.of("k1", "v1", "k2", "v2"));
+	}
+
+	private void assertRoundTrip(Object value) throws Exception {
+		Map<String, Object> claims = new HashMap<>();
+		claims.put("value", value);
+		String json = this.mapper.writeValueAsString(claims);
+		Map<String, Object> deserialized = this.mapper.readValue(json, MAP_TYPE);
+		assertThat(deserialized.get("value")).isEqualTo(value);
+	}
+
+}
diff --git a/oauth2/oauth2-authorization-server/src/test/java/org/springframework/security/oauth2/server/authorization/JdbcOAuth2AuthorizationServiceTests.java b/oauth2/oauth2-authorization-server/src/test/java/org/springframework/security/oauth2/server/authorization/JdbcOAuth2AuthorizationServiceTests.java
index 04f7a9a3103..048593a7aca 100644
--- a/oauth2/oauth2-authorization-server/src/test/java/org/springframework/security/oauth2/server/authorization/JdbcOAuth2AuthorizationServiceTests.java
+++ b/oauth2/oauth2-authorization-server/src/test/java/org/springframework/security/oauth2/server/authorization/JdbcOAuth2AuthorizationServiceTests.java
@@ -29,6 +29,7 @@
 import java.util.Map;
 import java.util.Set;
 import java.util.function.Function;
+import java.util.stream.Stream;
 
 import org.junit.jupiter.api.AfterEach;
 import org.junit.jupiter.api.BeforeEach;
@@ -355,6 +356,30 @@ public void findByTokenWhenAccessTokenExistsThenFound() {
 		assertThat(authorization).isEqualTo(result);
 	}
 
+	// gh-20084
+	@Test
+	public void findByTokenWhenAccessTokenClaimsContainImmutableCollectionsThenFound() {
+		given(this.registeredClientRepository.findById(eq(REGISTERED_CLIENT.getId()))).willReturn(REGISTERED_CLIENT);
+		OAuth2AccessToken accessToken = new OAuth2AccessToken(OAuth2AccessToken.TokenType.BEARER, "access-token",
+				Instant.now().minusSeconds(60).truncatedTo(ChronoUnit.MILLIS),
+				Instant.now().truncatedTo(ChronoUnit.MILLIS));
+		Map<String, Object> claims = Map.of("roles", Stream.of("ROLE_USER", "ROLE_ADMIN").toList(), "scope",
+				Set.of("read", "write"), "aud", List.of("client"), "attributes", Map.of("k", "v"));
+		OAuth2Authorization authorization = OAuth2Authorization.withRegisteredClient(REGISTERED_CLIENT)
+			.id(ID)
+			.principalName(PRINCIPAL_NAME)
+			.authorizationGrantType(AUTHORIZATION_GRANT_TYPE)
+			.token(AUTHORIZATION_CODE)
+			.token(accessToken, (metadata) -> metadata.put(OAuth2Authorization.Token.CLAIMS_METADATA_NAME, claims))
+			.build();
+		this.authorizationService.save(authorization);
+
+		OAuth2Authorization result = this.authorizationService.findByToken(accessToken.getTokenValue(),
+				OAuth2TokenType.ACCESS_TOKEN);
+		assertThat(result).isNotNull();
+		assertThat(result.getAccessToken().getClaims()).isEqualTo(claims);
+	}
+
 	@Test
 	public void findByTokenWhenIdTokenExistsThenFound() {
 		given(this.registeredClientRepository.findById(eq(REGISTERED_CLIENT.getId()))).willReturn(REGISTERED_CLIENT);