diff --git a/src/main/java/org/springframework/data/jpa/support/MergingPersistenceUnitManager.java b/src/main/java/org/springframework/data/jpa/support/MergingPersistenceUnitManager.java
index bdf531d62..eae8cc1db 100644
--- a/src/main/java/org/springframework/data/jpa/support/MergingPersistenceUnitManager.java
+++ b/src/main/java/org/springframework/data/jpa/support/MergingPersistenceUnitManager.java
@@ -1,5 +1,5 @@
 /*
- * Copyright 2011 the original author or authors.
+ * Copyright 2011-2012 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.
@@ -57,6 +57,14 @@ public class MergingPersistenceUnitManager extends DefaultPersistenceUnitManager
 		}
 	}
 
+	/* 
+	 * (non-Javadoc)
+	 * @see org.springframework.orm.jpa.persistenceunit.DefaultPersistenceUnitManager#isPersistenceUnitOverrideAllowed()
+	 */
+	protected boolean isPersistenceUnitOverrideAllowed() {
+		return true;
+	}
+
 	void postProcessPersistenceUnitInfo(MutablePersistenceUnitInfo pui, PersistenceUnitInfo oldPui) {
 
 		for (URL url : oldPui.getJarFileUrls()) {
@@ -68,6 +76,14 @@ public class MergingPersistenceUnitManager extends DefaultPersistenceUnitManager
 			}
 		}
 
+		for (String className : oldPui.getManagedClassNames()) {
+
+			if (!pui.getManagedClassNames().contains(className)) {
+				log.debug("Adding class {} to PersistenceUnit {}", className, pui.getPersistenceUnitName());
+				pui.addManagedClassName(className);
+			}
+		}
+
 		pui.addJarFileUrl(oldPui.getPersistenceUnitRootUrl());
 	}
 }
diff --git a/src/test/java/org/springframework/data/jpa/support/MergingPersistenceUnitManagerUnitTests.java b/src/test/java/org/springframework/data/jpa/support/MergingPersistenceUnitManagerUnitTests.java
index 193670973..cb6b771f4 100644
--- a/src/test/java/org/springframework/data/jpa/support/MergingPersistenceUnitManagerUnitTests.java
+++ b/src/test/java/org/springframework/data/jpa/support/MergingPersistenceUnitManagerUnitTests.java
@@ -1,5 +1,5 @@
 /*
- * Copyright 2011 the original author or authors.
+ * Copyright 2011-2012 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.
@@ -15,6 +15,8 @@
  */
 package org.springframework.data.jpa.support;
 
+import static org.hamcrest.Matchers.*;
+import static org.junit.Assert.*;
 import static org.mockito.Mockito.*;
 
 import java.net.MalformedURLException;
@@ -27,6 +29,8 @@ import org.junit.Test;
 import org.junit.runner.RunWith;
 import org.mockito.Mock;
 import org.mockito.runners.MockitoJUnitRunner;
+import org.springframework.data.jpa.domain.sample.Role;
+import org.springframework.data.jpa.domain.sample.User;
 import org.springframework.orm.jpa.persistenceunit.MutablePersistenceUnitInfo;
 
 /**
@@ -53,4 +57,17 @@ public class MergingPersistenceUnitManagerUnitTests {
 		manager.postProcessPersistenceUnitInfo(newInfo, oldInfo);
 		verify(newInfo).addJarFileUrl(jarFileUrl);
 	}
+
+	@Test
+	public void mergesManagedClassesCorrectly() {
+
+		MergingPersistenceUnitManager manager = new MergingPersistenceUnitManager();
+		manager.setPersistenceXmlLocations(new String[] { "classpath:org/springframework/data/jpa/support/persistence.xml",
+				"classpath:org/springframework/data/jpa/support/persistence2.xml" });
+		manager.preparePersistenceUnitInfos();
+
+		PersistenceUnitInfo info = manager.obtainPersistenceUnitInfo("pu");
+		assertThat(info.getManagedClassNames().size(), is(2));
+		assertThat(info.getManagedClassNames(), hasItems(User.class.getName(), Role.class.getName()));
+	}
 }
diff --git a/src/test/resources/org/springframework/data/jpa/support/persistence.xml b/src/test/resources/org/springframework/data/jpa/support/persistence.xml
new file mode 100644
index 000000000..230d4bb2a
--- /dev/null
+++ b/src/test/resources/org/springframework/data/jpa/support/persistence.xml
@@ -0,0 +1,6 @@
+<?xml version="1.0" encoding="UTF-8"?>
+<persistence version="1.0" xmlns="http://java.sun.com/xml/ns/persistence" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:schemaLocation="http://java.sun.com/xml/ns/persistence http://java.sun.com/xml/ns/persistence/persistence_1_0.xsd">
+	<persistence-unit name="pu">
+		<class>org.springframework.data.jpa.domain.sample.User</class>
+	</persistence-unit>
+</persistence>
diff --git a/src/test/resources/org/springframework/data/jpa/support/persistence2.xml b/src/test/resources/org/springframework/data/jpa/support/persistence2.xml
new file mode 100644
index 000000000..756e2aa4a
--- /dev/null
+++ b/src/test/resources/org/springframework/data/jpa/support/persistence2.xml
@@ -0,0 +1,6 @@
+<?xml version="1.0" encoding="UTF-8"?>
+<persistence version="1.0" xmlns="http://java.sun.com/xml/ns/persistence" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:schemaLocation="http://java.sun.com/xml/ns/persistence http://java.sun.com/xml/ns/persistence/persistence_1_0.xsd">
+	<persistence-unit name="pu">
+		<class>org.springframework.data.jpa.domain.sample.Role</class>
+	</persistence-unit>
+</persistence>