diff --git a/spring-boot-project/spring-boot/src/main/java/org/springframework/boot/context/properties/source/ConfigurationPropertySources.java b/spring-boot-project/spring-boot/src/main/java/org/springframework/boot/context/properties/source/ConfigurationPropertySources.java
index 4e57523359..002c9e084d 100644
--- a/spring-boot-project/spring-boot/src/main/java/org/springframework/boot/context/properties/source/ConfigurationPropertySources.java
+++ b/spring-boot-project/spring-boot/src/main/java/org/springframework/boot/context/properties/source/ConfigurationPropertySources.java
@@ -1,5 +1,5 @@
 /*
- * Copyright 2012-2017 the original author or authors.
+ * Copyright 2012-2018 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.
@@ -73,7 +73,12 @@ public final class ConfigurationPropertySources {
 		Assert.isInstanceOf(ConfigurableEnvironment.class, environment);
 		MutablePropertySources sources = ((ConfigurableEnvironment) environment)
 				.getPropertySources();
-		if (!sources.contains(ATTACHED_PROPERTY_SOURCE_NAME)) {
+		PropertySource<?> attached = sources.get(ATTACHED_PROPERTY_SOURCE_NAME);
+		if (attached != null && attached.getSource() != sources) {
+			sources.remove(ATTACHED_PROPERTY_SOURCE_NAME);
+			attached = null;
+		}
+		if (attached == null) {
 			sources.addFirst(new ConfigurationPropertySourcesPropertySource(
 					ATTACHED_PROPERTY_SOURCE_NAME,
 					new SpringConfigurationPropertySources(sources)));
diff --git a/spring-boot-project/spring-boot/src/test/java/org/springframework/boot/context/properties/source/ConfigurationPropertySourcesTests.java b/spring-boot-project/spring-boot/src/test/java/org/springframework/boot/context/properties/source/ConfigurationPropertySourcesTests.java
index 02f7b48538..1feaaaf079 100644
--- a/spring-boot-project/spring-boot/src/test/java/org/springframework/boot/context/properties/source/ConfigurationPropertySourcesTests.java
+++ b/spring-boot-project/spring-boot/src/test/java/org/springframework/boot/context/properties/source/ConfigurationPropertySourcesTests.java
@@ -1,5 +1,5 @@
 /*
- * Copyright 2012-2017 the original author or authors.
+ * Copyright 2012-2018 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.
@@ -56,6 +56,19 @@ public class ConfigurationPropertySourcesTests {
 		assertThat(resolver.getProperty("server.port")).isEqualTo("1234");
 	}
 
+	@Test
+	public void attachShouldReAttachInMergedSetup() {
+		ConfigurableEnvironment parent = new StandardEnvironment();
+		ConfigurationPropertySources.attach(parent);
+		parent.getProperty("my.example-property");
+		ConfigurableEnvironment child = new StandardEnvironment();
+		child.merge(parent);
+		child.getPropertySources().addLast(new MapPropertySource("config",
+				Collections.singletonMap("my.example_property", "1234")));
+		ConfigurationPropertySources.attach(child);
+		assertThat(child.getProperty("my.example-property")).isEqualTo("1234");
+	}
+
 	@Test
 	public void getWhenNotAttachedShouldReturnAdapted() {
 		ConfigurableEnvironment environment = new StandardEnvironment();