diff --git a/spring-boot-project/spring-boot/src/main/java/org/springframework/boot/SpringApplication.java b/spring-boot-project/spring-boot/src/main/java/org/springframework/boot/SpringApplication.java
index 6887d07fef..5ca1aa695e 100644
--- a/spring-boot-project/spring-boot/src/main/java/org/springframework/boot/SpringApplication.java
+++ b/spring-boot-project/spring-boot/src/main/java/org/springframework/boot/SpringApplication.java
@@ -341,6 +341,7 @@ public class SpringApplication {
 		// Create and configure the environment
 		ConfigurableEnvironment environment = getOrCreateEnvironment();
 		configureEnvironment(environment, applicationArguments.getSourceArgs());
+		ConfigurationPropertySources.attach(environment);
 		listeners.environmentPrepared(environment);
 		bindToSpringApplication(environment);
 		if (!this.isCustomEnvironment) {
diff --git a/spring-boot-project/spring-boot/src/test/java/org/springframework/boot/SpringApplicationTests.java b/spring-boot-project/spring-boot/src/test/java/org/springframework/boot/SpringApplicationTests.java
index 52f960a0e4..9575deb03d 100644
--- a/spring-boot-project/spring-boot/src/test/java/org/springframework/boot/SpringApplicationTests.java
+++ b/spring-boot-project/spring-boot/src/test/java/org/springframework/boot/SpringApplicationTests.java
@@ -1085,6 +1085,14 @@ class SpringApplicationTests {
 				.getBean("someBean")).isEqualTo("override");
 	}
 
+	@Test
+	void relaxedBindingShouldWorkBeforeEnvironmentIsPrepared() {
+		SpringApplication application = new SpringApplication(ExampleConfig.class);
+		application.setWebApplicationType(WebApplicationType.NONE);
+		this.context = application.run("--spring.config.additionalLocation=classpath:custom-config/");
+		assertThat(this.context.getEnvironment().getProperty("hello")).isEqualTo("world");
+	}
+
 	@Test
 	void lazyInitializationIsDisabledByDefault() {
 		assertThat(new SpringApplication(LazyInitializationConfig.class).run("--spring.main.web-application-type=none")
diff --git a/spring-boot-project/spring-boot/src/test/resources/custom-config/application.yml b/spring-boot-project/spring-boot/src/test/resources/custom-config/application.yml
new file mode 100644
index 0000000000..bb56b05514
--- /dev/null
+++ b/spring-boot-project/spring-boot/src/test/resources/custom-config/application.yml
@@ -0,0 +1 @@
+hello: world