diff --git a/spring-test/src/main/java/org/springframework/mock/web/MockMultipartHttpServletRequest.java b/spring-test/src/main/java/org/springframework/mock/web/MockMultipartHttpServletRequest.java
index 935d66aee71..f9607f5bb2f 100644
--- a/spring-test/src/main/java/org/springframework/mock/web/MockMultipartHttpServletRequest.java
+++ b/spring-test/src/main/java/org/springframework/mock/web/MockMultipartHttpServletRequest.java
@@ -1,5 +1,5 @@
 /*
- * Copyright 2002-2018 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.
@@ -16,6 +16,7 @@
 
 package org.springframework.mock.web;
 
+import java.io.IOException;
 import java.util.Collections;
 import java.util.Enumeration;
 import java.util.Iterator;
@@ -23,6 +24,8 @@ import java.util.List;
 import java.util.Map;
 
 import javax.servlet.ServletContext;
+import javax.servlet.ServletException;
+import javax.servlet.http.Part;
 
 import org.springframework.http.HttpHeaders;
 import org.springframework.http.HttpMethod;
@@ -121,9 +124,17 @@ public class MockMultipartHttpServletRequest extends MockHttpServletRequest impl
 		if (file != null) {
 			return file.getContentType();
 		}
-		else {
-			return null;
+		try {
+			Part part = getPart(paramOrFileName);
+			if (part != null) {
+				return part.getContentType();
+			}
+		}
+		catch (ServletException | IOException ex) {
+			// Should never happen (we're not actually parsing)
+			throw new IllegalStateException(ex);
 		}
+		return null;
 	}
 
 	@Override
@@ -147,7 +158,7 @@ public class MockMultipartHttpServletRequest extends MockHttpServletRequest impl
 		String contentType = getMultipartContentType(paramOrFileName);
 		if (contentType != null) {
 			HttpHeaders headers = new HttpHeaders();
-			headers.add("Content-Type", contentType);
+			headers.add(HttpHeaders.CONTENT_TYPE, contentType);
 			return headers;
 		}
 		else {
diff --git a/spring-web/src/test/java/org/springframework/mock/web/test/MockMultipartHttpServletRequest.java b/spring-web/src/test/java/org/springframework/mock/web/test/MockMultipartHttpServletRequest.java
index 7aeab6f98bf..d96a29b4168 100644
--- a/spring-web/src/test/java/org/springframework/mock/web/test/MockMultipartHttpServletRequest.java
+++ b/spring-web/src/test/java/org/springframework/mock/web/test/MockMultipartHttpServletRequest.java
@@ -1,5 +1,5 @@
 /*
- * Copyright 2002-2018 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.
@@ -16,6 +16,7 @@
 
 package org.springframework.mock.web.test;
 
+import java.io.IOException;
 import java.util.Collections;
 import java.util.Enumeration;
 import java.util.Iterator;
@@ -23,6 +24,8 @@ import java.util.List;
 import java.util.Map;
 
 import javax.servlet.ServletContext;
+import javax.servlet.ServletException;
+import javax.servlet.http.Part;
 
 import org.springframework.http.HttpHeaders;
 import org.springframework.http.HttpMethod;
@@ -121,9 +124,17 @@ public class MockMultipartHttpServletRequest extends MockHttpServletRequest impl
 		if (file != null) {
 			return file.getContentType();
 		}
-		else {
-			return null;
+		try {
+			Part part = getPart(paramOrFileName);
+			if (part != null) {
+				return part.getContentType();
+			}
+		}
+		catch (ServletException | IOException ex) {
+			// Should never happen (we're not actually parsing)
+			throw new IllegalStateException(ex);
 		}
+		return null;
 	}
 
 	@Override
@@ -147,7 +158,7 @@ public class MockMultipartHttpServletRequest extends MockHttpServletRequest impl
 		String contentType = getMultipartContentType(paramOrFileName);
 		if (contentType != null) {
 			HttpHeaders headers = new HttpHeaders();
-			headers.add("Content-Type", contentType);
+			headers.add(HttpHeaders.CONTENT_TYPE, contentType);
 			return headers;
 		}
 		else {
diff --git a/spring-web/src/test/java/org/springframework/web/multipart/support/RequestPartServletServerHttpRequestTests.java b/spring-web/src/test/java/org/springframework/web/multipart/support/RequestPartServletServerHttpRequestTests.java
index a42d1b335e8..87082cc8bcf 100644
--- a/spring-web/src/test/java/org/springframework/web/multipart/support/RequestPartServletServerHttpRequestTests.java
+++ b/spring-web/src/test/java/org/springframework/web/multipart/support/RequestPartServletServerHttpRequestTests.java
@@ -139,23 +139,13 @@ public class RequestPartServletServerHttpRequestTests {
 		assertArrayEquals(bytes, result);
 	}
 
-	@Test
+	@Test  // gh-25829
 	public void getBodyViaRequestPart() throws Exception {
-		MockMultipartHttpServletRequest mockRequest = new MockMultipartHttpServletRequest() {
-			@Override
-			public HttpHeaders getMultipartHeaders(String paramOrFileName) {
-				HttpHeaders headers = new HttpHeaders();
-				headers.setContentType(MediaType.APPLICATION_OCTET_STREAM);
-				return headers;
-			}
-		};
-
 		byte[] bytes = "content".getBytes("UTF-8");
 		MockPart mockPart = new MockPart("part", bytes);
 		mockPart.getHeaders().setContentType(MediaType.APPLICATION_JSON);
-		mockRequest.addPart(mockPart);
-		mockRequest.addPart(mockPart);
-		ServerHttpRequest request = new RequestPartServletServerHttpRequest(mockRequest, "part");
+		this.mockRequest.addPart(mockPart);
+		ServerHttpRequest request = new RequestPartServletServerHttpRequest(this.mockRequest, "part");
 
 		byte[] result = FileCopyUtils.copyToByteArray(request.getBody());
 		assertArrayEquals(bytes, result);