diff --git a/spring-test/src/main/java/org/springframework/test/util/AopTestUtils.java b/spring-test/src/main/java/org/springframework/test/util/AopTestUtils.java
index f49b30551c0..4eda8a45ac2 100644
--- a/spring-test/src/main/java/org/springframework/test/util/AopTestUtils.java
+++ b/spring-test/src/main/java/org/springframework/test/util/AopTestUtils.java
@@ -18,6 +18,7 @@ package org.springframework.test.util;
 
 import org.springframework.aop.framework.Advised;
 import org.springframework.aop.support.AopUtils;
+import org.springframework.util.Assert;
 
 /**
  * {@code AopTestUtils} is a collection of AOP-related utility methods for
@@ -41,7 +42,8 @@ public class AopTestUtils {
 	 * be returned; otherwise, the {@code candidate} will be returned
 	 * <em>as is</em>.
 	 *
-	 * @param candidate the instance to check (potentially a Spring AOP proxy)
+	 * @param candidate the instance to check (potentially a Spring AOP proxy);
+	 * never {@code null}
 	 * @return the target object or the {@code candidate}; never {@code null}
 	 * @throws IllegalStateException if an error occurs while unwrapping a proxy
 	 * @see Advised#getTargetSource()
@@ -49,6 +51,7 @@ public class AopTestUtils {
 	 */
 	@SuppressWarnings("unchecked")
 	public static <T> T getTargetObject(Object candidate) {
+		Assert.notNull(candidate, "candidate must not be null");
 		try {
 			if (AopUtils.isAopProxy(candidate) && (candidate instanceof Advised)) {
 				return (T) ((Advised) candidate).getTargetSource().getTarget();
@@ -57,8 +60,6 @@ public class AopTestUtils {
 		catch (Exception e) {
 			throw new IllegalStateException("Failed to unwrap proxied object.", e);
 		}
-
-		// else
 		return (T) candidate;
 	}
 
@@ -71,7 +72,8 @@ public class AopTestUtils {
 	 * nested proxies will be returned; otherwise, the {@code candidate}
 	 * will be returned <em>as is</em>.
 	 *
-	 * @param candidate the instance to check (potentially a Spring AOP proxy)
+	 * @param candidate the instance to check (potentially a Spring AOP proxy);
+	 * never {@code null}
 	 * @return the ultimate target object or the {@code candidate}; never
 	 * {@code null}
 	 * @throws IllegalStateException if an error occurs while unwrapping a proxy
@@ -80,6 +82,7 @@ public class AopTestUtils {
 	 */
 	@SuppressWarnings("unchecked")
 	public static <T> T getUltimateTargetObject(Object candidate) {
+		Assert.notNull(candidate, "candidate must not be null");
 		try {
 			if (AopUtils.isAopProxy(candidate) && (candidate instanceof Advised)) {
 				return (T) getUltimateTargetObject(((Advised) candidate).getTargetSource().getTarget());
@@ -88,8 +91,6 @@ public class AopTestUtils {
 		catch (Exception e) {
 			throw new IllegalStateException("Failed to unwrap proxied object.", e);
 		}
-
-		// else
 		return (T) candidate;
 	}
 
diff --git a/spring-test/src/test/java/org/springframework/test/util/AopTestUtilsTests.java b/spring-test/src/test/java/org/springframework/test/util/AopTestUtilsTests.java
index 21070c5646a..dac809f4ea4 100644
--- a/spring-test/src/test/java/org/springframework/test/util/AopTestUtilsTests.java
+++ b/spring-test/src/test/java/org/springframework/test/util/AopTestUtilsTests.java
@@ -36,6 +36,11 @@ public class AopTestUtilsTests {
 	private final FooImpl foo = new FooImpl();
 
 
+	@Test(expected = IllegalArgumentException.class)
+	public void getTargetObjectForNull() {
+		getTargetObject(null);
+	}
+
 	@Test
 	public void getTargetObjectForNonProxiedObject() {
 		Foo target = getTargetObject(foo);
@@ -66,6 +71,11 @@ public class AopTestUtilsTests {
 		assertNotSame(foo, target);
 	}
 
+	@Test(expected = IllegalArgumentException.class)
+	public void getUltimateTargetObjectForNull() {
+		getUltimateTargetObject(null);
+	}
+
 	@Test
 	public void getUltimateTargetObjectForNonProxiedObject() {
 		Foo target = getUltimateTargetObject(foo);