diff --git a/spring-webmvc/src/main/java/org/springframework/web/servlet/resource/ResourceUrlEncodingFilter.java b/spring-webmvc/src/main/java/org/springframework/web/servlet/resource/ResourceUrlEncodingFilter.java
index c2a4486a3fd..ffdc573a328 100644
--- a/spring-webmvc/src/main/java/org/springframework/web/servlet/resource/ResourceUrlEncodingFilter.java
+++ b/spring-webmvc/src/main/java/org/springframework/web/servlet/resource/ResourceUrlEncodingFilter.java
@@ -162,6 +162,11 @@ public class ResourceUrlEncodingFilter extends GenericFilterBean {
 	}
 
 
+	/**
+	 * Runtime exception to get far enough (to ResourceUrlProviderExposingInterceptor)
+	 * where it can be re-thrown as ServletRequestBindingException to result in
+	 * a 400 response.
+	 */
 	@SuppressWarnings("serial")
 	static class LookupPathIndexException extends IllegalArgumentException {