diff --git a/spring-test/src/main/java/org/springframework/mock/web/MockServletContext.java b/spring-test/src/main/java/org/springframework/mock/web/MockServletContext.java
index e7b0b7737f6..ecab0ecf3ce 100644
--- a/spring-test/src/main/java/org/springframework/mock/web/MockServletContext.java
+++ b/spring-test/src/main/java/org/springframework/mock/web/MockServletContext.java
@@ -50,6 +50,7 @@ import org.springframework.http.MediaType;
 import org.springframework.http.MediaTypeFactory;
 import org.springframework.util.Assert;
 import org.springframework.util.ClassUtils;
+import org.springframework.util.MimeType;
 import org.springframework.util.ObjectUtils;
 import org.springframework.util.StringUtils;
 import org.springframework.web.util.WebUtils;
@@ -267,7 +268,9 @@ public class MockServletContext implements ServletContext {
 			return this.mimeTypes.get(extension).toString();
 		}
 		else {
-			return MediaTypeFactory.getMediaType(filePath).orElse(MediaType.APPLICATION_OCTET_STREAM).toString();
+			return MediaTypeFactory.getMediaType(filePath).
+					map(MimeType::toString)
+					.orElse(null);
 		}
 	}
 
diff --git a/spring-test/src/test/java/org/springframework/mock/web/MockServletContextTests.java b/spring-test/src/test/java/org/springframework/mock/web/MockServletContextTests.java
index acc7081ec0f..2ac2fd5c719 100644
--- a/spring-test/src/test/java/org/springframework/mock/web/MockServletContextTests.java
+++ b/spring-test/src/test/java/org/springframework/mock/web/MockServletContextTests.java
@@ -82,6 +82,7 @@ public class MockServletContextTests {
 	public void getMimeType() {
 		assertEquals("text/html", sc.getMimeType("test.html"));
 		assertEquals("image/gif", sc.getMimeType("test.gif"));
+		assertNull(sc.getMimeType("test.foobar"));
 	}
 
 	/**
diff --git a/spring-web/src/test/java/org/springframework/mock/web/test/MockServletContext.java b/spring-web/src/test/java/org/springframework/mock/web/test/MockServletContext.java
index 6dcacadcd93..2a7500551b8 100644
--- a/spring-web/src/test/java/org/springframework/mock/web/test/MockServletContext.java
+++ b/spring-web/src/test/java/org/springframework/mock/web/test/MockServletContext.java
@@ -50,6 +50,7 @@ import org.springframework.http.MediaType;
 import org.springframework.http.MediaTypeFactory;
 import org.springframework.util.Assert;
 import org.springframework.util.ClassUtils;
+import org.springframework.util.MimeType;
 import org.springframework.util.ObjectUtils;
 import org.springframework.util.StringUtils;
 import org.springframework.web.util.WebUtils;
@@ -266,7 +267,9 @@ public class MockServletContext implements ServletContext {
 			return this.mimeTypes.get(extension).toString();
 		}
 		else {
-			return MediaTypeFactory.getMediaType(filePath).orElse(MediaType.APPLICATION_OCTET_STREAM).toString();
+			return MediaTypeFactory.getMediaType(filePath).
+					map(MimeType::toString)
+					.orElse(null);
 		}
 	}