diff --git a/spring-webflux/src/main/kotlin/org/springframework/web/reactive/function/server/RouterFunctionDsl.kt b/spring-webflux/src/main/kotlin/org/springframework/web/reactive/function/server/RouterFunctionDsl.kt
index 61803b8695..1cee19ecef 100644
--- a/spring-webflux/src/main/kotlin/org/springframework/web/reactive/function/server/RouterFunctionDsl.kt
+++ b/spring-webflux/src/main/kotlin/org/springframework/web/reactive/function/server/RouterFunctionDsl.kt
@@ -21,6 +21,7 @@ import org.springframework.http.HttpMethod
 import org.springframework.http.HttpStatus
 import org.springframework.http.MediaType
 import reactor.core.publisher.Mono
+import reactor.core.publisher.cast
 import java.net.URI
 
 /**
@@ -153,8 +154,8 @@ open class RouterFunctionDsl(private val init: RouterFunctionDsl.() -> Unit) : (
 	 * Route to the given handler function if the given request predicate applies.
 	 * @see RouterFunctions.route
 	 */
-	fun GET(pattern: String, f: (ServerRequest) -> Mono<ServerResponse>) {
-		routes += RouterFunctions.route(RequestPredicates.GET(pattern), HandlerFunction { f(it) })
+	fun GET(pattern: String, f: (ServerRequest) -> Mono<out ServerResponse>) {
+		routes += RouterFunctions.route(RequestPredicates.GET(pattern), HandlerFunction<ServerResponse> { f(it).cast() })
 	}
 
 	/**
@@ -168,8 +169,8 @@ open class RouterFunctionDsl(private val init: RouterFunctionDsl.() -> Unit) : (
 	 * Route to the given handler function if the given request predicate applies.
 	 * @see RouterFunctions.route
 	 */
-	fun HEAD(pattern: String, f: (ServerRequest) -> Mono<ServerResponse>) {
-		routes += RouterFunctions.route(RequestPredicates.HEAD(pattern), HandlerFunction { f(it) })
+	fun HEAD(pattern: String, f: (ServerRequest) -> Mono<out ServerResponse>) {
+		routes += RouterFunctions.route(RequestPredicates.HEAD(pattern), HandlerFunction<ServerResponse> { f(it).cast() })
 	}
 
 	/**
@@ -183,8 +184,8 @@ open class RouterFunctionDsl(private val init: RouterFunctionDsl.() -> Unit) : (
 	 * Route to the given handler function if the given POST predicate applies.
 	 * @see RouterFunctions.route
 	 */
-	fun POST(pattern: String, f: (ServerRequest) -> Mono<ServerResponse>) {
-		routes += RouterFunctions.route(RequestPredicates.POST(pattern), HandlerFunction { f(it) })
+	fun POST(pattern: String, f: (ServerRequest) -> Mono<out ServerResponse>) {
+		routes += RouterFunctions.route(RequestPredicates.POST(pattern), HandlerFunction<ServerResponse> { f(it).cast() })
 	}
 
 	/**
@@ -198,8 +199,8 @@ open class RouterFunctionDsl(private val init: RouterFunctionDsl.() -> Unit) : (
 	 * Route to the given handler function if the given PUT predicate applies.
 	 * @see RouterFunctions.route
 	 */
-	fun PUT(pattern: String, f: (ServerRequest) -> Mono<ServerResponse>) {
-		routes += RouterFunctions.route(RequestPredicates.PUT(pattern), HandlerFunction { f(it) })
+	fun PUT(pattern: String, f: (ServerRequest) -> Mono<out ServerResponse>) {
+		routes += RouterFunctions.route(RequestPredicates.PUT(pattern), HandlerFunction<ServerResponse> { f(it).cast() })
 	}
 
 	/**
@@ -213,8 +214,8 @@ open class RouterFunctionDsl(private val init: RouterFunctionDsl.() -> Unit) : (
 	 * Route to the given handler function if the given PATCH predicate applies.
 	 * @see RouterFunctions.route
 	 */
-	fun PATCH(pattern: String, f: (ServerRequest) -> Mono<ServerResponse>) {
-		routes += RouterFunctions.route(RequestPredicates.PATCH(pattern), HandlerFunction { f(it) })
+	fun PATCH(pattern: String, f: (ServerRequest) -> Mono<out ServerResponse>) {
+		routes += RouterFunctions.route(RequestPredicates.PATCH(pattern), HandlerFunction<ServerResponse> { f(it).cast() })
 	}
 
 	/**
@@ -230,8 +231,8 @@ open class RouterFunctionDsl(private val init: RouterFunctionDsl.() -> Unit) : (
 	 * Route to the given handler function if the given DELETE predicate applies.
 	 * @see RouterFunctions.route
 	 */
-	fun DELETE(pattern: String, f: (ServerRequest) -> Mono<ServerResponse>) {
-		routes += RouterFunctions.route(RequestPredicates.DELETE(pattern), HandlerFunction { f(it) })
+	fun DELETE(pattern: String, f: (ServerRequest) -> Mono<out ServerResponse>) {
+		routes += RouterFunctions.route(RequestPredicates.DELETE(pattern), HandlerFunction<ServerResponse> { f(it).cast() })
 	}
 
 	/**
@@ -247,8 +248,8 @@ open class RouterFunctionDsl(private val init: RouterFunctionDsl.() -> Unit) : (
 	 * Route to the given handler function if the given OPTIONS predicate applies.
 	 * @see RouterFunctions.route
 	 */
-	fun OPTIONS(pattern: String, f: (ServerRequest) -> Mono<ServerResponse>) {
-		routes += RouterFunctions.route(RequestPredicates.OPTIONS(pattern), HandlerFunction { f(it) })
+	fun OPTIONS(pattern: String, f: (ServerRequest) -> Mono<out ServerResponse>) {
+		routes += RouterFunctions.route(RequestPredicates.OPTIONS(pattern), HandlerFunction<ServerResponse> { f(it).cast() })
 	}
 
 	/**
@@ -264,8 +265,8 @@ open class RouterFunctionDsl(private val init: RouterFunctionDsl.() -> Unit) : (
 	 * Route to the given handler function if the given accept predicate applies.
 	 * @see RouterFunctions.route
 	 */
-	fun accept(mediaType: MediaType, f: (ServerRequest) -> Mono<ServerResponse>) {
-		routes += RouterFunctions.route(RequestPredicates.accept(mediaType), HandlerFunction { f(it) })
+	fun accept(mediaType: MediaType, f: (ServerRequest) -> Mono<out ServerResponse>) {
+		routes += RouterFunctions.route(RequestPredicates.accept(mediaType), HandlerFunction<ServerResponse> { f(it).cast() })
 	}
 
 	/**
@@ -281,8 +282,8 @@ open class RouterFunctionDsl(private val init: RouterFunctionDsl.() -> Unit) : (
 	 * Route to the given handler function if the given contentType predicate applies.
 	 * @see RouterFunctions.route
 	 */
-	fun contentType(mediaType: MediaType, f: (ServerRequest) -> Mono<ServerResponse>) {
-		routes += RouterFunctions.route(RequestPredicates.contentType(mediaType), HandlerFunction { f(it) })
+	fun contentType(mediaType: MediaType, f: (ServerRequest) -> Mono<out ServerResponse>) {
+		routes += RouterFunctions.route(RequestPredicates.contentType(mediaType), HandlerFunction<ServerResponse> { f(it).cast() })
 	}
 
 	/**
@@ -298,8 +299,8 @@ open class RouterFunctionDsl(private val init: RouterFunctionDsl.() -> Unit) : (
 	 * Route to the given handler function if the given headers predicate applies.
 	 * @see RouterFunctions.route
 	 */
-	fun headers(headersPredicate: (ServerRequest.Headers) -> Boolean, f: (ServerRequest) -> Mono<ServerResponse>) {
-		routes += RouterFunctions.route(RequestPredicates.headers(headersPredicate), HandlerFunction { f(it) })
+	fun headers(headersPredicate: (ServerRequest.Headers) -> Boolean, f: (ServerRequest) -> Mono<out ServerResponse>) {
+		routes += RouterFunctions.route(RequestPredicates.headers(headersPredicate), HandlerFunction<ServerResponse> { f(it).cast() })
 	}
 
 	/**
@@ -314,8 +315,8 @@ open class RouterFunctionDsl(private val init: RouterFunctionDsl.() -> Unit) : (
 	 * Route to the given handler function if the given method predicate applies.
 	 * @see RouterFunctions.route
 	 */
-	fun method(httpMethod: HttpMethod, f: (ServerRequest) -> Mono<ServerResponse>) {
-		routes += RouterFunctions.route(RequestPredicates.method(httpMethod), HandlerFunction { f(it) })
+	fun method(httpMethod: HttpMethod, f: (ServerRequest) -> Mono<out ServerResponse>) {
+		routes += RouterFunctions.route(RequestPredicates.method(httpMethod), HandlerFunction<ServerResponse> { f(it).cast() })
 	}
 
 	/**
@@ -329,8 +330,8 @@ open class RouterFunctionDsl(private val init: RouterFunctionDsl.() -> Unit) : (
 	 * Route to the given handler function if the given path predicate applies.
 	 * @see RouterFunctions.route
 	 */
-	fun path(pattern: String, f: (ServerRequest) -> Mono<ServerResponse>) {
-		routes += RouterFunctions.route(RequestPredicates.path(pattern), HandlerFunction { f(it) })
+	fun path(pattern: String, f: (ServerRequest) -> Mono<out ServerResponse>) {
+		routes += RouterFunctions.route(RequestPredicates.path(pattern), HandlerFunction<ServerResponse> { f(it).cast() })
 	}
 
 	/**
@@ -343,8 +344,8 @@ open class RouterFunctionDsl(private val init: RouterFunctionDsl.() -> Unit) : (
 	 * Route to the given handler function if the given pathExtension predicate applies.
 	 * @see RouterFunctions.route
 	 */
-	fun pathExtension(extension: String, f: (ServerRequest) -> Mono<ServerResponse>) {
-		routes += RouterFunctions.route(RequestPredicates.pathExtension(extension), HandlerFunction { f(it) })
+	fun pathExtension(extension: String, f: (ServerRequest) -> Mono<out ServerResponse>) {
+		routes += RouterFunctions.route(RequestPredicates.pathExtension(extension), HandlerFunction<ServerResponse> { f(it).cast() })
 	}
 
 	/**
@@ -358,8 +359,8 @@ open class RouterFunctionDsl(private val init: RouterFunctionDsl.() -> Unit) : (
 	 * Route to the given handler function if the given pathExtension predicate applies.
 	 * @see RouterFunctions.route
 	 */
-	fun pathExtension(predicate: (String) -> Boolean, f: (ServerRequest) -> Mono<ServerResponse>) {
-		routes += RouterFunctions.route(RequestPredicates.pathExtension(predicate), HandlerFunction { f(it) })
+	fun pathExtension(predicate: (String) -> Boolean, f: (ServerRequest) -> Mono<out ServerResponse>) {
+		routes += RouterFunctions.route(RequestPredicates.pathExtension(predicate), HandlerFunction<ServerResponse> { f(it).cast() })
 	}
 
 	/**
@@ -374,8 +375,8 @@ open class RouterFunctionDsl(private val init: RouterFunctionDsl.() -> Unit) : (
 	 * Route to the given handler function if the given queryParam predicate applies.
 	 * @see RouterFunctions.route
 	 */
-	fun queryParam(name: String, predicate: (String) -> Boolean, f: (ServerRequest) -> Mono<ServerResponse>) {
-		routes += RouterFunctions.route(RequestPredicates.queryParam(name, predicate), HandlerFunction { f(it) })
+	fun queryParam(name: String, predicate: (String) -> Boolean, f: (ServerRequest) -> Mono<out ServerResponse>) {
+		routes += RouterFunctions.route(RequestPredicates.queryParam(name, predicate), HandlerFunction<ServerResponse> { f(it).cast() })
 	}
 
 	/**
@@ -393,8 +394,8 @@ open class RouterFunctionDsl(private val init: RouterFunctionDsl.() -> Unit) : (
 	 * Route to the given handler function if the given request predicate applies.
 	 * @see RouterFunctions.route
 	 */
-	operator fun RequestPredicate.invoke(f: (ServerRequest) -> Mono<ServerResponse>) {
-		routes += RouterFunctions.route(this, HandlerFunction { f(it) })
+	operator fun RequestPredicate.invoke(f: (ServerRequest) -> Mono<out ServerResponse>) {
+		routes += RouterFunctions.route(this, HandlerFunction<ServerResponse> { f(it).cast() })
 	}
 
 	/**
@@ -402,8 +403,8 @@ open class RouterFunctionDsl(private val init: RouterFunctionDsl.() -> Unit) : (
 	 * processed as a path predicate) applies.
 	 * @see RouterFunctions.route
 	 */
-	operator fun String.invoke(f: (ServerRequest) -> Mono<ServerResponse>) {
-		routes += RouterFunctions.route(RequestPredicates.path(this),  HandlerFunction { f(it) })
+	operator fun String.invoke(f: (ServerRequest) -> Mono<out ServerResponse>) {
+		routes += RouterFunctions.route(RequestPredicates.path(this),  HandlerFunction<ServerResponse> { f(it).cast() })
 	}
 
 	/**
diff --git a/spring-webflux/src/test/kotlin/org/springframework/web/reactive/function/server/RouterFunctionDslTests.kt b/spring-webflux/src/test/kotlin/org/springframework/web/reactive/function/server/RouterFunctionDslTests.kt
index 2eceb5b59f..ce32b91b77 100644
--- a/spring-webflux/src/test/kotlin/org/springframework/web/reactive/function/server/RouterFunctionDslTests.kt
+++ b/spring-webflux/src/test/kotlin/org/springframework/web/reactive/function/server/RouterFunctionDslTests.kt
@@ -1,5 +1,5 @@
 /*
- * Copyright 2002-2017 the original author or authors.
+ * Copyright 2002-2018 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.
@@ -43,7 +43,7 @@ class RouterFunctionDslTests {
 
 	@Test
 	fun accept() {
-		val request = builder().header(ACCEPT, APPLICATION_ATOM_XML_VALUE).build()
+		val request = builder().uri(URI("/content")).header(ACCEPT, APPLICATION_ATOM_XML_VALUE).build()
 		StepVerifier.create(sampleRouter().route(request))
 				.expectNextCount(1)
 				.verifyComplete()
@@ -63,7 +63,7 @@ class RouterFunctionDslTests {
 
 	@Test
 	fun contentType() {
-		val request = builder().header(CONTENT_TYPE, APPLICATION_OCTET_STREAM_VALUE).build()
+		val request = builder().uri(URI("/content")).header(CONTENT_TYPE, APPLICATION_OCTET_STREAM_VALUE).build()
 		StepVerifier.create(sampleRouter().route(request))
 				.expectNextCount(1)
 				.verifyComplete()
@@ -112,6 +112,14 @@ class RouterFunctionDslTests {
 				.verifyComplete()
 	}
 
+	@Test
+	fun rendering() {
+		val request = builder().uri(URI("/rendering")).build()
+		StepVerifier.create(sampleRouter().route(request).flatMap { it.handle(request) })
+				.expectNextMatches { it is RenderingResponse}
+				.verifyComplete()
+	}
+
 
 	private fun sampleRouter() = router {
 		(GET("/foo/") or GET("/foos/")) { req -> handle(req) }
@@ -123,8 +131,10 @@ class RouterFunctionDslTests {
 			}
 			"/foo/"  { handleFromClass(it) }
 		}
-		accept(APPLICATION_ATOM_XML, ::handle)
-		contentType(APPLICATION_OCTET_STREAM, ::handle)
+		"/content".nest {
+			accept(APPLICATION_ATOM_XML, ::handle)
+			contentType(APPLICATION_OCTET_STREAM, ::handle)
+		}
 		method(PATCH, ::handle)
 		headers { it.accept().contains(APPLICATION_JSON) }.nest {
 			GET("/api/foo/", ::handle)
@@ -141,6 +151,7 @@ class RouterFunctionDslTests {
 			}
 		}
 		path("/baz", ::handle)
+		GET("/rendering") { RenderingResponse.create("index").build() }
 	}
 }