diff --git a/spring-webflux/src/main/java/org/springframework/web/reactive/function/BodyInserters.java b/spring-webflux/src/main/java/org/springframework/web/reactive/function/BodyInserters.java
index 56f1b41d78a..15f6ad99fa0 100644
--- a/spring-webflux/src/main/java/org/springframework/web/reactive/function/BodyInserters.java
+++ b/spring-webflux/src/main/java/org/springframework/web/reactive/function/BodyInserters.java
@@ -1,5 +1,5 @@
 /*
- * Copyright 2002-2019 the original author or authors.
+ * Copyright 2002-2020 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.
@@ -218,7 +218,8 @@ public abstract class BodyInserters {
 		return (outputMessage, context) -> {
 			ResolvableType elementType = RESOURCE_TYPE;
 			HttpMessageWriter<Resource> writer = findWriter(context, elementType, null);
-			return write(Mono.just(resource), elementType, null, outputMessage, context, writer);
+			MediaType contentType = outputMessage.getHeaders().getContentType();
+			return write(Mono.just(resource), elementType, contentType, outputMessage, context, writer);
 		};
 	}
 
diff --git a/spring-webflux/src/test/java/org/springframework/web/reactive/function/BodyInsertersTests.java b/spring-webflux/src/test/java/org/springframework/web/reactive/function/BodyInsertersTests.java
index 11141262083..bc68dc96d9a 100644
--- a/spring-webflux/src/test/java/org/springframework/web/reactive/function/BodyInsertersTests.java
+++ b/spring-webflux/src/test/java/org/springframework/web/reactive/function/BodyInsertersTests.java
@@ -1,5 +1,5 @@
 /*
- * Copyright 2002-2019 the original author or authors.
+ * Copyright 2002-2020 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.
@@ -48,6 +48,7 @@ import org.springframework.core.io.buffer.DefaultDataBufferFactory;
 import org.springframework.core.testfixture.io.buffer.DataBufferTestUtils;
 import org.springframework.http.HttpMethod;
 import org.springframework.http.HttpRange;
+import org.springframework.http.MediaType;
 import org.springframework.http.ReactiveHttpOutputMessage;
 import org.springframework.http.client.reactive.ClientHttpRequest;
 import org.springframework.http.codec.EncoderHttpMessageWriter;
@@ -224,14 +225,13 @@ public class BodyInsertersTests {
 
 	@Test
 	public void ofResource() throws IOException {
-		Resource body = new ClassPathResource("response.txt", getClass());
-		BodyInserter<Resource, ReactiveHttpOutputMessage> inserter = BodyInserters.fromResource(body);
+		Resource resource = new ClassPathResource("response.txt", getClass());
 
 		MockServerHttpResponse response = new MockServerHttpResponse();
-		Mono<Void> result = inserter.insert(response, this.context);
+		Mono<Void> result = BodyInserters.fromResource(resource).insert(response, this.context);
 		StepVerifier.create(result).expectComplete().verify();
 
-		byte[] expectedBytes = Files.readAllBytes(body.getFile().toPath());
+		byte[] expectedBytes = Files.readAllBytes(resource.getFile().toPath());
 
 		StepVerifier.create(response.getBody())
 				.consumeNextWith(dataBuffer -> {
@@ -244,6 +244,29 @@ public class BodyInsertersTests {
 				.verify();
 	}
 
+	@Test // gh-24366
+	public void ofResourceWithExplicitMediaType() throws IOException {
+		Resource resource = new ClassPathResource("response.txt", getClass());
+
+		MockClientHttpRequest request = new MockClientHttpRequest(HttpMethod.POST, "/");
+		request.getHeaders().setContentType(MediaType.TEXT_MARKDOWN);
+		Mono<Void> result = BodyInserters.fromResource(resource).insert(request, this.context);
+		StepVerifier.create(result).expectComplete().verify();
+
+		byte[] expectedBytes = Files.readAllBytes(resource.getFile().toPath());
+
+		assertThat(request.getHeaders().getContentType()).isEqualTo(MediaType.TEXT_MARKDOWN);
+		StepVerifier.create(request.getBody())
+				.consumeNextWith(dataBuffer -> {
+					byte[] resultBytes = new byte[dataBuffer.readableByteCount()];
+					dataBuffer.read(resultBytes);
+					DataBufferUtils.release(dataBuffer);
+					assertThat(resultBytes).isEqualTo(expectedBytes);
+				})
+				.expectComplete()
+				.verify();
+	}
+
 	@Test
 	public void ofResourceRange() throws IOException {
 		final int rangeStart = 10;