diff --git a/spring-modulith-test/src/main/java/org/springframework/modulith/test/ModuleTestAutoConfiguration.java b/spring-modulith-test/src/main/java/org/springframework/modulith/test/ModuleTestAutoConfiguration.java
index 237b4917..86aad2c8 100644
--- a/spring-modulith-test/src/main/java/org/springframework/modulith/test/ModuleTestAutoConfiguration.java
+++ b/spring-modulith-test/src/main/java/org/springframework/modulith/test/ModuleTestAutoConfiguration.java
@@ -43,8 +43,8 @@ import org.springframework.util.StringUtils;
 @AutoConfigureOrder(Ordered.HIGHEST_PRECEDENCE)
 class ModuleTestAutoConfiguration {
 
-	private static final String AUTOCONFIG_PACKAGES = "org.springframework.boot.autoconfigure.AutoConfigurationPackages";
-	private static final String ENTITY_SCAN_PACKAGE = "org.springframework.boot.autoconfigure.domain.EntityScanPackages";
+	static final String AUTOCONFIG_PACKAGES = "org.springframework.boot.autoconfigure.AutoConfigurationPackages";
+	static final String ENTITY_SCAN_PACKAGE = "org.springframework.boot.autoconfigure.domain.EntityScanPackages";
 
 	static class AutoConfigurationAndEntityScanPackageCustomizer implements ImportBeanDefinitionRegistrar {
 
@@ -67,7 +67,7 @@ class ModuleTestAutoConfiguration {
 			setBasePackagesOn(registry, ENTITY_SCAN_PACKAGE, basePackages);
 		}
 
-		private void setBasePackagesOn(BeanDefinitionRegistry registry, String beanName, List<String> packages) {
+		void setBasePackagesOn(BeanDefinitionRegistry registry, String beanName, List<String> packages) {
 
 			if (!registry.containsBeanDefinition(beanName)) {
 				return;
@@ -77,9 +77,11 @@ class ModuleTestAutoConfiguration {
 			var definition = registry.getBeanDefinition(beanName);
 			var holder = definition.getConstructorArgumentValues().getArgumentValue(0, String[].class);
 
-			Arrays.stream((String[]) holder.getValue())
-					.filter(it -> it.startsWith("org.springframework.modulith"))
-					.forEach(packagesToSet::add);
+			if (holder != null) {
+				Arrays.stream((String[]) holder.getValue())
+						.filter(it -> it.startsWith("org.springframework.modulith"))
+						.forEach(packagesToSet::add);
+			}
 
 			definition.getConstructorArgumentValues().addIndexedArgumentValue(0, packagesToSet.toArray(String[]::new));
 		}
diff --git a/spring-modulith-test/src/test/java/org/springframework/modulith/test/ModuleTestAutoConfigurationUnitTests.java b/spring-modulith-test/src/test/java/org/springframework/modulith/test/ModuleTestAutoConfigurationUnitTests.java
new file mode 100644
index 00000000..eda27e00
--- /dev/null
+++ b/spring-modulith-test/src/test/java/org/springframework/modulith/test/ModuleTestAutoConfigurationUnitTests.java
@@ -0,0 +1,46 @@
+/*
+ * Copyright 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.
+ * 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.modulith.test;
+
+import static org.assertj.core.api.Assertions.*;
+
+import java.util.Collections;
+
+import org.junit.jupiter.api.Test;
+import org.springframework.beans.factory.support.DefaultListableBeanFactory;
+import org.springframework.beans.factory.support.RootBeanDefinition;
+import org.springframework.boot.autoconfigure.AutoConfigurationPackages;
+
+/**
+ * Unit tests for {@link ModuleTestAutoConfiguration}.
+ *
+ * @author Oliver Drotbohm
+ */
+class ModuleTestAutoConfigurationUnitTests {
+
+	@Test // GH-453
+	void handlesNoConstructorArgumentOnPackagesBeanDefinition() {
+
+		var definition = new RootBeanDefinition(AutoConfigurationPackages.class);
+		var factory = new DefaultListableBeanFactory();
+		factory.registerBeanDefinition(ModuleTestAutoConfiguration.AUTOCONFIG_PACKAGES, definition);
+
+		assertThatNoException().isThrownBy(() -> {
+			new ModuleTestAutoConfiguration.AutoConfigurationAndEntityScanPackageCustomizer()
+					.setBasePackagesOn(factory, ModuleTestAutoConfiguration.AUTOCONFIG_PACKAGES, Collections.emptyList());
+		});
+	}
+}