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 38e991a8..237b4917 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
@@ -15,6 +15,7 @@
  */
 package org.springframework.modulith.test;
 
+import java.util.ArrayList;
 import java.util.Arrays;
 import java.util.List;
 
@@ -72,14 +73,15 @@ class ModuleTestAutoConfiguration {
 				return;
 			}
 
+			var packagesToSet = new ArrayList<>(packages);
 			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(packages::add);
+					.forEach(packagesToSet::add);
 
-			definition.getConstructorArgumentValues().addIndexedArgumentValue(0, packages.toArray(String[]::new));
+			definition.getConstructorArgumentValues().addIndexedArgumentValue(0, packagesToSet.toArray(String[]::new));
 		}
 	}
 }
diff --git a/spring-modulith-test/src/test/java/org/springframework/modulith/test/ModuleTestAutoConfigurationIntegrationTests.java b/spring-modulith-test/src/test/java/org/springframework/modulith/test/ModuleTestAutoConfigurationIntegrationTests.java
new file mode 100644
index 00000000..b3c9fbe2
--- /dev/null
+++ b/spring-modulith-test/src/test/java/org/springframework/modulith/test/ModuleTestAutoConfigurationIntegrationTests.java
@@ -0,0 +1,58 @@
+/*
+ * Copyright 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.
+ * 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 org.junit.jupiter.api.Test;
+import org.springframework.boot.autoconfigure.AutoConfigurations;
+import org.springframework.boot.autoconfigure.EnableAutoConfiguration;
+import org.springframework.boot.autoconfigure.SpringBootApplication;
+import org.springframework.boot.autoconfigure.domain.EntityScan;
+import org.springframework.boot.autoconfigure.domain.EntityScanPackages;
+import org.springframework.boot.test.context.runner.ApplicationContextRunner;
+
+/**
+ * Integration tests for {@link ModuleTestAutoConfiguration}.
+ *
+ * @author Oliver Drotbohm
+ */
+class ModuleTestAutoConfigurationIntegrationTests {
+
+	@Test // GH-345
+	void bootstrapsTestWithManualEntityScanOfModulithPackage() {
+
+		new ApplicationContextRunner()
+				.withBean(ModuleTestExecution.class, ModuleTestExecution.of(ModuleTest.class))
+				.withConfiguration(AutoConfigurations.of(ModuleTestAutoConfiguration.class))
+				.withUserConfiguration(ManualModulithEntityScan.class)
+				.run(ctx -> {
+
+					assertThat(ctx).hasNotFailed();
+					assertThat(ctx.getBean(EntityScanPackages.class).getPackageNames())
+							.containsExactlyInAnyOrder("org.springframework.modulith.test",
+									"org.springframework.modulith.events.jpa");
+				});
+	}
+
+	@SpringBootApplication
+	@ApplicationModuleTest
+	static class ModuleTest {}
+
+	@EnableAutoConfiguration
+	@EntityScan("org.springframework.modulith.events.jpa")
+	static class ManualModulithEntityScan {}
+}