diff --git a/spring-test/src/main/java/org/springframework/test/web/servlet/request/MockHttpServletRequestBuilder.java b/spring-test/src/main/java/org/springframework/test/web/servlet/request/MockHttpServletRequestBuilder.java
index ef178c394b..e315c948a8 100644
--- a/spring-test/src/main/java/org/springframework/test/web/servlet/request/MockHttpServletRequestBuilder.java
+++ b/spring-test/src/main/java/org/springframework/test/web/servlet/request/MockHttpServletRequestBuilder.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.
@@ -145,7 +145,14 @@ public class MockHttpServletRequestBuilder
 	 * @param vars zero or more URI variables
 	 */
 	MockHttpServletRequestBuilder(HttpMethod httpMethod, String url, Object... vars) {
-		this(httpMethod.name(), UriComponentsBuilder.fromUriString(url).buildAndExpand(vars).encode().toUri());
+		this(httpMethod.name(), initUri(url, vars));
+	}
+
+	private static URI initUri(String url, Object[] vars) {
+		Assert.notNull(url, "'url' must not be null");
+		Assert.isTrue(url.startsWith("/") || url.startsWith("http://") || url.startsWith("https://"), "" +
+				"'url' should start with a path or be a complete HTTP URL: " + url);
+		return UriComponentsBuilder.fromUriString(url).buildAndExpand(vars).encode().toUri();
 	}
 
 	/**
diff --git a/spring-test/src/test/java/org/springframework/test/web/servlet/request/MockHttpServletRequestBuilderTests.java b/spring-test/src/test/java/org/springframework/test/web/servlet/request/MockHttpServletRequestBuilderTests.java
index 17fb123ace..47f51e1046 100644
--- a/spring-test/src/test/java/org/springframework/test/web/servlet/request/MockHttpServletRequestBuilderTests.java
+++ b/spring-test/src/test/java/org/springframework/test/web/servlet/request/MockHttpServletRequestBuilderTests.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.
@@ -49,6 +49,7 @@ import org.springframework.web.servlet.support.SessionFlashMapManager;
 import org.springframework.web.util.UriComponentsBuilder;
 
 import static org.assertj.core.api.Assertions.assertThat;
+import static org.assertj.core.api.Assertions.assertThatIllegalArgumentException;
 
 /**
  * Unit tests for building a {@link MockHttpServletRequest} with
@@ -88,7 +89,8 @@ public class MockHttpServletRequestBuilderTests {
 		assertThat(request.getServerName()).isEqualTo("java.sun.com");
 		assertThat(request.getServerPort()).isEqualTo(8080);
 		assertThat(request.getRequestURI()).isEqualTo("/javase/6/docs/api/java/util/BitSet.html");
-		assertThat(request.getRequestURL().toString()).isEqualTo("https://java.sun.com:8080/javase/6/docs/api/java/util/BitSet.html");
+		assertThat(request.getRequestURL().toString())
+				.isEqualTo("https://java.sun.com:8080/javase/6/docs/api/java/util/BitSet.html");
 	}
 
 	@Test
@@ -107,6 +109,12 @@ public class MockHttpServletRequestBuilderTests {
 		assertThat(request.getRequestURI()).isEqualTo("/test//currentlyValid/0");
 	}
 
+	@Test // gh-24556
+	public void requestUriWithoutScheme() {
+		assertThatIllegalArgumentException().isThrownBy(() -> MockMvcRequestBuilders.get("localhost:8080/path"))
+				.withMessage("'url' should start with a path or be a complete HTTP URL: localhost:8080/path");
+	}
+
 	@Test
 	public void contextPathEmpty() {
 		this.builder = new MockHttpServletRequestBuilder(HttpMethod.GET, "/foo");