diff --git a/spring-boot-project/spring-boot/src/main/java/org/springframework/boot/DefaultPropertiesPropertySource.java b/spring-boot-project/spring-boot/src/main/java/org/springframework/boot/DefaultPropertiesPropertySource.java
index b5be872bf43..36affd9eab2 100644
--- a/spring-boot-project/spring-boot/src/main/java/org/springframework/boot/DefaultPropertiesPropertySource.java
+++ b/spring-boot-project/spring-boot/src/main/java/org/springframework/boot/DefaultPropertiesPropertySource.java
@@ -16,6 +16,7 @@
 
 package org.springframework.boot;
 
+import java.util.HashMap;
 import java.util.Map;
 import java.util.function.Consumer;
 
@@ -72,6 +73,40 @@ public class DefaultPropertiesPropertySource extends MapPropertySource {
 		}
 	}
 
+	/**
+	 * Add a new {@link DefaultPropertiesPropertySource} or merge with an existing one.
+	 * @param source the {@code Map} source
+	 * @param sources the existing sources
+	 * @since 2.4.4
+	 */
+	public static void addOrMerge(Map<String, Object> source, MutablePropertySources sources) {
+		if (!CollectionUtils.isEmpty(source)) {
+			Map<String, Object> resultingSource = new HashMap<>();
+			DefaultPropertiesPropertySource propertySource = new DefaultPropertiesPropertySource(resultingSource);
+			if (sources.contains(NAME)) {
+				mergeIfPossible(source, sources, resultingSource);
+				sources.replace(NAME, propertySource);
+			}
+			else {
+				resultingSource.putAll(source);
+				sources.addLast(propertySource);
+			}
+		}
+	}
+
+	@SuppressWarnings("unchecked")
+	private static void mergeIfPossible(Map<String, Object> source, MutablePropertySources sources,
+			Map<String, Object> resultingSource) {
+		PropertySource<?> existingSource = sources.get(NAME);
+		if (existingSource != null) {
+			Object underlyingSource = existingSource.getSource();
+			if (underlyingSource instanceof Map) {
+				resultingSource.putAll((Map<String, Object>) underlyingSource);
+			}
+			resultingSource.putAll(source);
+		}
+	}
+
 	/**
 	 * Move the 'defaultProperties' property source so that it's the last source in the
 	 * given {@link ConfigurableEnvironment}.
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 9b2b0c9b7c1..65f33e71f6d 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
@@ -518,7 +518,9 @@ public class SpringApplication {
 	 */
 	protected void configurePropertySources(ConfigurableEnvironment environment, String[] args) {
 		MutablePropertySources sources = environment.getPropertySources();
-		DefaultPropertiesPropertySource.ifNotEmpty(this.defaultProperties, sources::addLast);
+		if (!CollectionUtils.isEmpty(this.defaultProperties)) {
+			DefaultPropertiesPropertySource.addOrMerge(this.defaultProperties, sources);
+		}
 		if (this.addCommandLineProperties && args.length > 0) {
 			String name = CommandLinePropertySource.COMMAND_LINE_PROPERTY_SOURCE_NAME;
 			if (sources.contains(name)) {
diff --git a/spring-boot-project/spring-boot/src/test/java/org/springframework/boot/DefaultPropertiesPropertySourceTests.java b/spring-boot-project/spring-boot/src/test/java/org/springframework/boot/DefaultPropertiesPropertySourceTests.java
index ad43f3e5c9d..e375847d81e 100644
--- a/spring-boot-project/spring-boot/src/test/java/org/springframework/boot/DefaultPropertiesPropertySourceTests.java
+++ b/spring-boot-project/spring-boot/src/test/java/org/springframework/boot/DefaultPropertiesPropertySourceTests.java
@@ -26,6 +26,7 @@ import org.mockito.Captor;
 import org.mockito.Mock;
 import org.mockito.junit.jupiter.MockitoExtension;
 
+import org.springframework.core.env.CompositePropertySource;
 import org.springframework.core.env.MutablePropertySources;
 import org.springframework.core.env.PropertySource;
 import org.springframework.mock.env.MockEnvironment;
@@ -39,6 +40,7 @@ import static org.mockito.Mockito.verifyNoInteractions;
  * Tests for {@link DefaultPropertiesPropertySource}.
  *
  * @author Phillip Webb
+ * @author Madhura Bhave
  */
 @ExtendWith(MockitoExtension.class)
 class DefaultPropertiesPropertySourceTests {
@@ -104,6 +106,39 @@ class DefaultPropertiesPropertySourceTests {
 		DefaultPropertiesPropertySource.moveToEnd(environment);
 	}
 
+	@Test
+	void addOrMergeWhenExistingNotFoundShouldAdd() {
+		MockEnvironment environment = new MockEnvironment();
+		MutablePropertySources propertySources = environment.getPropertySources();
+		DefaultPropertiesPropertySource.addOrMerge(Collections.singletonMap("spring", "boot"), propertySources);
+		assertThat(propertySources.contains(DefaultPropertiesPropertySource.NAME)).isTrue();
+		assertThat(propertySources.get(DefaultPropertiesPropertySource.NAME).getProperty("spring")).isEqualTo("boot");
+	}
+
+	@Test
+	void addOrMergeWhenExistingFoundShouldMerge() {
+		MockEnvironment environment = new MockEnvironment();
+		MutablePropertySources propertySources = environment.getPropertySources();
+		propertySources.addLast(new DefaultPropertiesPropertySource(Collections.singletonMap("spring", "boot")));
+		DefaultPropertiesPropertySource.addOrMerge(Collections.singletonMap("hello", "world"), propertySources);
+		assertThat(propertySources.contains(DefaultPropertiesPropertySource.NAME)).isTrue();
+		assertThat(propertySources.get(DefaultPropertiesPropertySource.NAME).getProperty("spring")).isEqualTo("boot");
+		assertThat(propertySources.get(DefaultPropertiesPropertySource.NAME).getProperty("hello")).isEqualTo("world");
+	}
+
+	@Test
+	void addOrMergeWhenExistingNotMapPropertySourceShouldNotMerge() {
+		MockEnvironment environment = new MockEnvironment();
+		MutablePropertySources propertySources = environment.getPropertySources();
+		CompositePropertySource composite = new CompositePropertySource(DefaultPropertiesPropertySource.NAME);
+		composite.addPropertySource(new DefaultPropertiesPropertySource(Collections.singletonMap("spring", "boot")));
+		propertySources.addFirst(composite);
+		DefaultPropertiesPropertySource.addOrMerge(Collections.singletonMap("hello", "world"), propertySources);
+		assertThat(propertySources.contains(DefaultPropertiesPropertySource.NAME)).isTrue();
+		assertThat(propertySources.get(DefaultPropertiesPropertySource.NAME).getProperty("spring")).isNull();
+		assertThat(propertySources.get(DefaultPropertiesPropertySource.NAME).getProperty("hello")).isEqualTo("world");
+	}
+
 	@Test
 	void moveToEndWhenPresentMovesToEnd() {
 		MockEnvironment environment = new MockEnvironment();
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 1b04c70fdcf..b818d3bcb53 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
@@ -53,6 +53,7 @@ import org.springframework.boot.availability.AvailabilityChangeEvent;
 import org.springframework.boot.availability.AvailabilityState;
 import org.springframework.boot.availability.LivenessState;
 import org.springframework.boot.availability.ReadinessState;
+import org.springframework.boot.builder.SpringApplicationBuilder;
 import org.springframework.boot.context.event.ApplicationContextInitializedEvent;
 import org.springframework.boot.context.event.ApplicationEnvironmentPreparedEvent;
 import org.springframework.boot.context.event.ApplicationFailedEvent;
@@ -105,6 +106,7 @@ import org.springframework.core.io.ResourceLoader;
 import org.springframework.core.metrics.ApplicationStartup;
 import org.springframework.core.metrics.StartupStep;
 import org.springframework.http.server.reactive.HttpHandler;
+import org.springframework.mock.env.MockEnvironment;
 import org.springframework.test.context.support.TestPropertySourceUtils;
 import org.springframework.util.LinkedMultiValueMap;
 import org.springframework.util.MultiValueMap;
@@ -887,6 +889,18 @@ class SpringApplicationTests {
 		assertThat(getEnvironment().getProperty("baz")).isEqualTo("");
 	}
 
+	@Test
+	void defaultPropertiesShouldBeMerged() {
+		MockEnvironment environment = new MockEnvironment();
+		environment.getPropertySources().addFirst(
+				new MapPropertySource(DefaultPropertiesPropertySource.NAME, Collections.singletonMap("bar", "foo")));
+		SpringApplication application = new SpringApplicationBuilder(ExampleConfig.class).environment(environment)
+				.properties("baz=bing").web(WebApplicationType.NONE).build();
+		this.context = application.run();
+		assertThat(getEnvironment().getProperty("bar")).isEqualTo("foo");
+		assertThat(getEnvironment().getProperty("baz")).isEqualTo("bing");
+	}
+
 	@Test
 	void commandLineArgsApplyToSpringApplication() {
 		TestSpringApplication application = new TestSpringApplication(ExampleConfig.class);