diff --git a/spring-web/src/test/java/org/springframework/http/server/reactive/MultipartIntegrationTests.java b/spring-web/src/test/java/org/springframework/http/server/reactive/MultipartIntegrationTests.java
index a756612bc8..23ef03e8fa 100644
--- a/spring-web/src/test/java/org/springframework/http/server/reactive/MultipartIntegrationTests.java
+++ b/spring-web/src/test/java/org/springframework/http/server/reactive/MultipartIntegrationTests.java
@@ -20,9 +20,9 @@ import java.net.URI;
 
 import org.junit.Test;
 import reactor.core.publisher.Mono;
+import reactor.test.StepVerifier;
 
 import org.springframework.core.io.ClassPathResource;
-import org.springframework.core.io.buffer.DataBuffer;
 import org.springframework.core.io.buffer.DataBufferUtils;
 import org.springframework.http.HttpEntity;
 import org.springframework.http.HttpHeaders;
@@ -103,12 +103,15 @@ public class MultipartIntegrationTests extends AbstractHttpHandlerIntegrationTes
 			assertEquals("fooPart", part.name());
 			assertTrue(part instanceof FilePart);
 			assertEquals("foo.txt", ((FilePart) part).filename());
-			DataBufferUtils.join(part.content()).subscribe(buffer -> {
-				assertEquals(12, buffer.readableByteCount());
-				byte[] byteContent = new byte[12];
-				buffer.read(byteContent);
-				assertEquals("Lorem Ipsum.", new String(byteContent));
-			});
+
+			StepVerifier.create(DataBufferUtils.join(part.content()))
+					.consumeNextWith(buffer -> {
+						assertEquals(12, buffer.readableByteCount());
+						byte[] byteContent = new byte[12];
+						buffer.read(byteContent);
+						assertEquals("Lorem Ipsum.", new String(byteContent));
+					})
+					.verifyComplete();
 		}
 
 		private void assertBarPart(Part part) {
diff --git a/spring-webflux/src/main/java/org/springframework/web/reactive/result/method/SyncInvocableHandlerMethod.java b/spring-webflux/src/main/java/org/springframework/web/reactive/result/method/SyncInvocableHandlerMethod.java
index fe6057cf03..216ecf7a0c 100644
--- a/spring-webflux/src/main/java/org/springframework/web/reactive/result/method/SyncInvocableHandlerMethod.java
+++ b/spring-webflux/src/main/java/org/springframework/web/reactive/result/method/SyncInvocableHandlerMethod.java
@@ -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.
@@ -21,6 +21,8 @@ import java.util.ArrayList;
 import java.util.List;
 import java.util.stream.Collectors;
 
+import reactor.core.publisher.MonoProcessor;
+
 import org.springframework.core.DefaultParameterNameDiscoverer;
 import org.springframework.core.ParameterNameDiscoverer;
 import org.springframework.lang.Nullable;
@@ -98,8 +100,21 @@ public class SyncInvocableHandlerMethod extends HandlerMethod {
 	public HandlerResult invokeForHandlerResult(ServerWebExchange exchange,
 			BindingContext bindingContext, Object... providedArgs) {
 
-		// This will not block with only sync resolvers allowed
-		return this.delegate.invoke(exchange, bindingContext, providedArgs).block();
+		MonoProcessor<HandlerResult> processor = MonoProcessor.create();
+		this.delegate.invoke(exchange, bindingContext, providedArgs).subscribeWith(processor);
+
+		if (processor.isTerminated()) {
+			Throwable error = processor.getError();
+			if (error != null) {
+				throw (RuntimeException) error;
+			}
+			return processor.peek();
+		}
+		else {
+			// Should never happen...
+			throw new IllegalStateException(
+					"SyncInvocableHandlerMethod should have completed synchronously.");
+		}
 	}
 
 }
diff --git a/spring-webflux/src/test/java/org/springframework/web/reactive/result/method/annotation/MultipartIntegrationTests.java b/spring-webflux/src/test/java/org/springframework/web/reactive/result/method/annotation/MultipartIntegrationTests.java
index 1a35d49f6a..68ae16b741 100644
--- a/spring-webflux/src/test/java/org/springframework/web/reactive/result/method/annotation/MultipartIntegrationTests.java
+++ b/spring-webflux/src/test/java/org/springframework/web/reactive/result/method/annotation/MultipartIntegrationTests.java
@@ -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.
@@ -52,7 +52,7 @@ import org.springframework.web.reactive.function.client.ClientResponse;
 import org.springframework.web.reactive.function.client.WebClient;
 import org.springframework.web.server.adapter.WebHttpHandlerBuilder;
 
-import static org.junit.Assert.assertEquals;
+import static org.junit.Assert.*;
 
 public class MultipartIntegrationTests extends AbstractHttpHandlerIntegrationTests {
 
@@ -170,10 +170,19 @@ public class MultipartIntegrationTests extends AbstractHttpHandlerIntegrationTes
 
 			assertEquals("fieldValue", fieldPart.value());
 			assertEquals("fileParts:foo.txt", partDescription(fileParts));
-			assertEquals("fileParts:foo.txt", partDescription(filePartsMono.block()));
-			assertEquals("[fileParts:foo.txt,fileParts:logo.png]", partFluxDescription(filePartsFlux).block());
 			assertEquals("Jason", person.getName());
-			assertEquals("Jason", personMono.block().getName());
+
+			StepVerifier.create(partFluxDescription(filePartsFlux))
+					.consumeNextWith(content -> assertEquals("[fileParts:foo.txt,fileParts:logo.png]", content))
+					.verifyComplete();
+
+			StepVerifier.create(filePartsMono)
+					.consumeNextWith(filePart -> assertEquals("fileParts:foo.txt", partDescription(filePart)))
+					.verifyComplete();
+
+			StepVerifier.create(personMono)
+					.consumeNextWith(p -> assertEquals("Jason", p.getName()))
+					.verifyComplete();
 		}
 
 		@PostMapping("/requestBodyMap")