diff --git a/spring-boot-project/spring-boot-test/src/main/java/org/springframework/boot/test/mock/mockito/MockitoPostProcessor.java b/spring-boot-project/spring-boot-test/src/main/java/org/springframework/boot/test/mock/mockito/MockitoPostProcessor.java
index 334d90dcfb1..6b36e7f0c98 100644
--- a/spring-boot-project/spring-boot-test/src/main/java/org/springframework/boot/test/mock/mockito/MockitoPostProcessor.java
+++ b/spring-boot-project/spring-boot-test/src/main/java/org/springframework/boot/test/mock/mockito/MockitoPostProcessor.java
@@ -254,9 +254,8 @@ public class MockitoPostProcessor implements InstantiationAwareBeanPostProcessor
 		Class<?> type = resolvableType.resolve(Object.class);
 		for (String beanName : beanFactory.getBeanNamesForType(FactoryBean.class, true, false)) {
 			beanName = BeanFactoryUtils.transformedBeanName(beanName);
-			BeanDefinition beanDefinition = beanFactory.getBeanDefinition(beanName);
-			Object attribute = beanDefinition.getAttribute(FactoryBean.OBJECT_TYPE_ATTRIBUTE);
-			if (resolvableType.equals(attribute) || type.equals(attribute)) {
+			Class<?> producedType = beanFactory.getType(beanName, false);
+			if (type.equals(producedType)) {
 				beans.add(beanName);
 			}
 		}
diff --git a/spring-boot-project/spring-boot-test/src/test/java/org/springframework/boot/test/mock/mockito/SpyBeanOnTestFieldForExistingGenericBeanProducedByFactoryBeanIntegrationTests.java b/spring-boot-project/spring-boot-test/src/test/java/org/springframework/boot/test/mock/mockito/SpyBeanOnTestFieldForExistingGenericBeanProducedByFactoryBeanIntegrationTests.java
new file mode 100644
index 00000000000..b84a8f1dadd
--- /dev/null
+++ b/spring-boot-project/spring-boot-test/src/test/java/org/springframework/boot/test/mock/mockito/SpyBeanOnTestFieldForExistingGenericBeanProducedByFactoryBeanIntegrationTests.java
@@ -0,0 +1,93 @@
+/*
+ * Copyright 2012-2022 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.boot.test.mock.mockito;
+
+import org.junit.jupiter.api.Test;
+import org.junit.jupiter.api.extension.ExtendWith;
+import org.mockito.Mockito;
+
+import org.springframework.beans.factory.FactoryBean;
+import org.springframework.beans.factory.support.BeanDefinitionRegistry;
+import org.springframework.beans.factory.support.RootBeanDefinition;
+import org.springframework.boot.test.mock.mockito.example.ExampleGenericService;
+import org.springframework.boot.test.mock.mockito.example.SimpleExampleStringGenericService;
+import org.springframework.context.annotation.Configuration;
+import org.springframework.context.annotation.Import;
+import org.springframework.context.annotation.ImportBeanDefinitionRegistrar;
+import org.springframework.core.ResolvableType;
+import org.springframework.core.type.AnnotationMetadata;
+import org.springframework.test.context.junit.jupiter.SpringExtension;
+
+import static org.assertj.core.api.Assertions.assertThat;
+
+/**
+ * Test {@link SpyBean @SpyBean} on a test class field can be used to replace an existing
+ * bean with generics that's produced by a factory bean.
+ *
+ * @author Andy Wilkinson
+ */
+@ExtendWith(SpringExtension.class)
+class SpyBeanOnTestFieldForExistingGenericBeanProducedByFactoryBeanIntegrationTests {
+
+	// gh-40234
+
+	@SpyBean(name = "exampleService")
+	private ExampleGenericService<String> exampleService;
+
+	@Test
+	void testSpying() {
+		assertThat(Mockito.mockingDetails(this.exampleService).isSpy()).isTrue();
+		assertThat(Mockito.mockingDetails(this.exampleService).getMockCreationSettings().getSpiedInstance())
+			.isInstanceOf(SimpleExampleStringGenericService.class);
+	}
+
+	@Configuration(proxyBeanMethods = false)
+	@Import(FactoryBeanRegistrar.class)
+	static class SpyBeanOnTestFieldForExistingBeanConfig {
+
+	}
+
+	static class FactoryBeanRegistrar implements ImportBeanDefinitionRegistrar {
+
+		@Override
+		public void registerBeanDefinitions(AnnotationMetadata importingClassMetadata,
+				BeanDefinitionRegistry registry) {
+			RootBeanDefinition definition = new RootBeanDefinition(ExampleGenericServiceFactoryBean.class);
+			definition.setTargetType(ResolvableType.forClassWithGenerics(ExampleGenericServiceFactoryBean.class, null,
+					ExampleGenericService.class));
+			registry.registerBeanDefinition("exampleService", definition);
+		}
+
+	}
+
+	static class ExampleGenericServiceFactoryBean<T, U extends ExampleGenericService<T>> implements FactoryBean<U> {
+
+		@SuppressWarnings("unchecked")
+		@Override
+		public U getObject() throws Exception {
+			return (U) new SimpleExampleStringGenericService();
+		}
+
+		@Override
+		@SuppressWarnings("rawtypes")
+		public Class<ExampleGenericService> getObjectType() {
+			return ExampleGenericService.class;
+		}
+
+	}
+
+}