diff --git a/spring-test/src/main/java/org/springframework/test/web/servlet/htmlunit/HtmlUnitRequestBuilder.java b/spring-test/src/main/java/org/springframework/test/web/servlet/htmlunit/HtmlUnitRequestBuilder.java
index 6308d61603..99a30e1cee 100644
--- a/spring-test/src/main/java/org/springframework/test/web/servlet/htmlunit/HtmlUnitRequestBuilder.java
+++ b/spring-test/src/main/java/org/springframework/test/web/servlet/htmlunit/HtmlUnitRequestBuilder.java
@@ -16,11 +16,14 @@
 
 package org.springframework.test.web.servlet.htmlunit;
 
+import java.io.File;
+import java.io.IOException;
 import java.io.UnsupportedEncodingException;
 import java.net.URL;
 import java.net.URLDecoder;
 import java.nio.charset.Charset;
 import java.nio.charset.StandardCharsets;
+import java.nio.file.Files;
 import java.util.ArrayList;
 import java.util.Collections;
 import java.util.Enumeration;
@@ -39,6 +42,7 @@ import com.gargoylesoftware.htmlunit.CookieManager;
 import com.gargoylesoftware.htmlunit.FormEncodingType;
 import com.gargoylesoftware.htmlunit.WebClient;
 import com.gargoylesoftware.htmlunit.WebRequest;
+import com.gargoylesoftware.htmlunit.util.KeyDataPair;
 import com.gargoylesoftware.htmlunit.util.NameValuePair;
 
 import org.springframework.beans.Mergeable;
@@ -46,6 +50,7 @@ import org.springframework.http.MediaType;
 import org.springframework.lang.Nullable;
 import org.springframework.mock.web.MockHttpServletRequest;
 import org.springframework.mock.web.MockHttpSession;
+import org.springframework.mock.web.MockPart;
 import org.springframework.test.web.servlet.RequestBuilder;
 import org.springframework.test.web.servlet.SmartRequestBuilder;
 import org.springframework.test.web.servlet.request.MockHttpServletRequestBuilder;
@@ -115,8 +120,9 @@ final class HtmlUnitRequestBuilder implements RequestBuilder, Mergeable {
 		UriComponents uriComponents = uriComponents();
 		String path = uriComponents.getPath();
 
-		MockHttpServletRequest request = new HtmlUnitMockHttpServletRequest(
-				servletContext, httpMethod, (path != null ? path : ""));
+		MockHttpServletRequest request =
+				new HtmlUnitMockHttpServletRequest(servletContext, httpMethod, (path != null ? path : ""));
+
 		parent(request, this.parentBuilder);
 		String host = uriComponents.getHost();
 		request.setServerName(host != null ? host : "");  // needs to be first for additional headers
@@ -365,7 +371,15 @@ final class HtmlUnitRequestBuilder implements RequestBuilder, Mergeable {
 			});
 		});
 		for (NameValuePair param : this.webRequest.getRequestParameters()) {
-			request.addParameter(param.getName(), param.getValue());
+			if (param instanceof KeyDataPair) {
+				KeyDataPair pair = (KeyDataPair) param;
+				MockPart part = new MockPart(pair.getName(), pair.getFile().getName(), readAllBytes(pair.getFile()));
+				part.getHeaders().setContentType(MediaType.valueOf(pair.getMimeType()));
+				request.addPart(part);
+			}
+			else {
+				request.addParameter(param.getName(), param.getValue());
+			}
 		}
 	}
 
@@ -378,6 +392,15 @@ final class HtmlUnitRequestBuilder implements RequestBuilder, Mergeable {
 		}
 	}
 
+	private byte[] readAllBytes(File file) {
+		try {
+			return Files.readAllBytes(file.toPath());
+		}
+		catch (IOException ex) {
+			throw new IllegalStateException(ex);
+		}
+	}
+
 	private void servletPath(MockHttpServletRequest request, String requestPath) {
 		String servletPath = requestPath.substring(request.getContextPath().length());
 		request.setServletPath(servletPath);
diff --git a/spring-test/src/test/java/org/springframework/test/web/servlet/htmlunit/HtmlUnitRequestBuilderTests.java b/spring-test/src/test/java/org/springframework/test/web/servlet/htmlunit/HtmlUnitRequestBuilderTests.java
index d9711e0a98..ad84f9ad89 100644
--- a/spring-test/src/test/java/org/springframework/test/web/servlet/htmlunit/HtmlUnitRequestBuilderTests.java
+++ b/spring-test/src/test/java/org/springframework/test/web/servlet/htmlunit/HtmlUnitRequestBuilderTests.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.
@@ -28,17 +28,21 @@ import java.util.Map;
 import javax.servlet.ServletContext;
 import javax.servlet.http.Cookie;
 import javax.servlet.http.HttpSession;
+import javax.servlet.http.Part;
 
 import com.gargoylesoftware.htmlunit.FormEncodingType;
 import com.gargoylesoftware.htmlunit.HttpMethod;
 import com.gargoylesoftware.htmlunit.WebClient;
 import com.gargoylesoftware.htmlunit.WebRequest;
+import com.gargoylesoftware.htmlunit.util.KeyDataPair;
+import com.gargoylesoftware.htmlunit.util.MimeType;
 import com.gargoylesoftware.htmlunit.util.NameValuePair;
 import org.apache.commons.io.IOUtils;
 import org.apache.http.auth.UsernamePasswordCredentials;
 import org.junit.jupiter.api.BeforeEach;
 import org.junit.jupiter.api.Test;
 
+import org.springframework.core.io.ClassPathResource;
 import org.springframework.mock.web.MockHttpServletRequest;
 import org.springframework.mock.web.MockHttpSession;
 import org.springframework.mock.web.MockServletContext;
@@ -418,6 +422,25 @@ public class HtmlUnitRequestBuilderTests {
 		assertThat(actualRequest.getParameter("name2")).isEqualTo("value2");
 	}
 
+	@Test // gh-24926
+	public void buildRequestParameterMapViaWebRequestDotSetFileToUploadAsParameter() throws Exception {
+
+		webRequest.setRequestParameters(Collections.singletonList(
+				new KeyDataPair("key",
+						new ClassPathResource("org/springframework/test/web/htmlunit/test.txt").getFile(),
+						"test.txt", MimeType.TEXT_PLAIN, StandardCharsets.UTF_8)));
+
+		MockHttpServletRequest actualRequest = requestBuilder.buildRequest(servletContext);
+
+		assertThat(actualRequest.getParts().size()).isEqualTo(1);
+		Part part = actualRequest.getPart("key");
+		assertThat(part).isNotNull();
+		assertThat(part.getName()).isEqualTo("key");
+		assertThat(IOUtils.toString(part.getInputStream(), StandardCharsets.UTF_8)).isEqualTo("test file");
+		assertThat(part.getSubmittedFileName()).isEqualTo("test.txt");
+		assertThat(part.getContentType()).isEqualTo(MimeType.TEXT_PLAIN);
+	}
+
 	@Test
 	public void buildRequestParameterMapFromSingleQueryParam() throws Exception {
 		webRequest.setUrl(new URL("https://example.com/example/?name=value"));
diff --git a/spring-test/src/test/resources/org/springframework/test/web/htmlunit/test.txt b/spring-test/src/test/resources/org/springframework/test/web/htmlunit/test.txt
new file mode 100644
index 0000000000..bdf08de0f3
--- /dev/null
+++ b/spring-test/src/test/resources/org/springframework/test/web/htmlunit/test.txt
@@ -0,0 +1 @@
+test file
\ No newline at end of file