diff --git a/spring-orm/src/main/java/org/springframework/orm/jpa/vendor/EclipseLinkJpaDialect.java b/spring-orm/src/main/java/org/springframework/orm/jpa/vendor/EclipseLinkJpaDialect.java
index 30db932f16..4c0ab302aa 100644
--- a/spring-orm/src/main/java/org/springframework/orm/jpa/vendor/EclipseLinkJpaDialect.java
+++ b/spring-orm/src/main/java/org/springframework/orm/jpa/vendor/EclipseLinkJpaDialect.java
@@ -1,5 +1,5 @@
 /*
- * Copyright 2002-2018 the original author or authors.
+ * Copyright 2002-2023 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.
@@ -22,6 +22,7 @@ import java.sql.SQLException;
 import javax.persistence.EntityManager;
 import javax.persistence.PersistenceException;
 
+import org.eclipse.persistence.sessions.DatabaseLogin;
 import org.eclipse.persistence.sessions.UnitOfWork;
 
 import org.springframework.jdbc.datasource.ConnectionHandle;
@@ -78,19 +79,37 @@ public class EclipseLinkJpaDialect extends DefaultJpaDialect {
 	public Object beginTransaction(EntityManager entityManager, TransactionDefinition definition)
 			throws PersistenceException, SQLException, TransactionException {
 
-		if (definition.getIsolationLevel() != TransactionDefinition.ISOLATION_DEFAULT) {
+		int currentIsolationLevel = definition.getIsolationLevel();
+		if (currentIsolationLevel != TransactionDefinition.ISOLATION_DEFAULT) {
 			// Pass custom isolation level on to EclipseLink's DatabaseLogin configuration
-			// (since Spring 4.1.2)
+			// (since Spring 4.1.2 / revised in 5.3.28)
 			UnitOfWork uow = entityManager.unwrap(UnitOfWork.class);
-			uow.getLogin().setTransactionIsolation(definition.getIsolationLevel());
+			DatabaseLogin databaseLogin = uow.getLogin();
+			// Synchronize on shared DatabaseLogin instance (-> concurrent transactions)
+			synchronized (databaseLogin) {
+				int originalIsolationLevel = databaseLogin.getTransactionIsolation();
+				// Apply current isolation level value, if necessary.
+				if (currentIsolationLevel != originalIsolationLevel) {
+					databaseLogin.setTransactionIsolation(currentIsolationLevel);
+				}
+				// Transaction begin including enforced JDBC Connection access
+				// (picking up current isolation level from DatabaseLogin)
+				entityManager.getTransaction().begin();
+				uow.beginEarlyTransaction();
+				entityManager.unwrap(Connection.class);
+				// Restore original isolation level value, if necessary.
+				if (currentIsolationLevel != originalIsolationLevel) {
+					databaseLogin.setTransactionIsolation(originalIsolationLevel);
+				}
+			}
 		}
-
-		entityManager.getTransaction().begin();
-
-		if (!definition.isReadOnly() && !this.lazyDatabaseTransaction) {
-			// Begin an early transaction to force EclipseLink to get a JDBC Connection
-			// so that Spring can manage transactions with JDBC as well as EclipseLink.
-			entityManager.unwrap(UnitOfWork.class).beginEarlyTransaction();
+		else {
+			entityManager.getTransaction().begin();
+			if (!definition.isReadOnly() && !this.lazyDatabaseTransaction) {
+				// Begin an early transaction to force EclipseLink to get a JDBC Connection
+				// so that Spring can manage transactions with JDBC as well as EclipseLink.
+				entityManager.unwrap(UnitOfWork.class).beginEarlyTransaction();
+			}
 		}
 
 		return null;
diff --git a/spring-orm/src/test/java/org/springframework/orm/jpa/AbstractContainerEntityManagerFactoryIntegrationTests.java b/spring-orm/src/test/java/org/springframework/orm/jpa/AbstractContainerEntityManagerFactoryIntegrationTests.java
index 81c7b0b912..c403a9aa68 100644
--- a/spring-orm/src/test/java/org/springframework/orm/jpa/AbstractContainerEntityManagerFactoryIntegrationTests.java
+++ b/spring-orm/src/test/java/org/springframework/orm/jpa/AbstractContainerEntityManagerFactoryIntegrationTests.java
@@ -1,5 +1,5 @@
 /*
- * Copyright 2002-2022 the original author or authors.
+ * Copyright 2002-2023 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.
@@ -27,8 +27,10 @@ import javax.persistence.Query;
 import org.junit.jupiter.api.Test;
 
 import org.springframework.core.testfixture.io.SerializationTestUtils;
+import org.springframework.jdbc.datasource.DataSourceUtils;
 import org.springframework.orm.jpa.domain.DriversLicense;
 import org.springframework.orm.jpa.domain.Person;
+import org.springframework.transaction.TransactionDefinition;
 
 import static org.assertj.core.api.Assertions.assertThat;
 import static org.assertj.core.api.Assertions.assertThatException;
@@ -114,24 +116,34 @@ public abstract class AbstractContainerEntityManagerFactoryIntegrationTests
 	}
 
 	@Test
-	public void testLazyLoading() {
+	public void testLazyLoading() throws Exception {
 		try {
 			Person tony = new Person();
 			tony.setFirstName("Tony");
 			tony.setLastName("Blair");
 			tony.setDriversLicense(new DriversLicense("8439DK"));
 			sharedEntityManager.persist(tony);
+			assertThat(DataSourceUtils.getConnection(jdbcTemplate.getDataSource()).getTransactionIsolation())
+					.isEqualTo(TransactionDefinition.ISOLATION_READ_COMMITTED);
 			setComplete();
 			endTransaction();
 
+			transactionDefinition.setIsolationLevel(TransactionDefinition.ISOLATION_SERIALIZABLE);
 			startNewTransaction();
+			assertThat(DataSourceUtils.getConnection(jdbcTemplate.getDataSource()).getTransactionIsolation())
+					.isEqualTo(TransactionDefinition.ISOLATION_SERIALIZABLE);
 			sharedEntityManager.clear();
 			Person newTony = entityManagerFactory.createEntityManager().getReference(Person.class, tony.getId());
 			assertThat(tony).isNotSameAs(newTony);
 			endTransaction();
 
-			assertThat(newTony.getDriversLicense()).isNotNull();
+			transactionDefinition.setIsolationLevel(TransactionDefinition.ISOLATION_DEFAULT);
+			startNewTransaction();
+			assertThat(DataSourceUtils.getConnection(jdbcTemplate.getDataSource()).getTransactionIsolation())
+					.isEqualTo(TransactionDefinition.ISOLATION_READ_COMMITTED);
+			endTransaction();
 
+			assertThat(newTony.getDriversLicense()).isNotNull();
 			newTony.getDriversLicense().getSerialNumber();
 		}
 		finally {