diff --git a/spring-web/src/main/java/org/springframework/http/server/reactive/ReactorServerHttpRequest.java b/spring-web/src/main/java/org/springframework/http/server/reactive/ReactorServerHttpRequest.java
index d73e44b2df..51fb5b7239 100644
--- a/spring-web/src/main/java/org/springframework/http/server/reactive/ReactorServerHttpRequest.java
+++ b/spring-web/src/main/java/org/springframework/http/server/reactive/ReactorServerHttpRequest.java
@@ -20,6 +20,7 @@ import java.net.InetSocketAddress;
 import java.net.URI;
 import java.net.URISyntaxException;
 
+import io.netty.handler.codec.http.HttpHeaderNames;
 import io.netty.handler.codec.http.cookie.Cookie;
 import reactor.core.publisher.Flux;
 import reactor.ipc.netty.http.server.HttpServerRequest;
@@ -55,16 +56,39 @@ public class ReactorServerHttpRequest extends AbstractServerHttpRequest {
 		this.bufferFactory = bufferFactory;
 	}
 
-	private static URI initUri(HttpServerRequest channel) throws URISyntaxException {
-		Assert.notNull(channel, "'channel' must not be null");
-		InetSocketAddress address = channel.remoteAddress();
-		String requestUri = channel.uri();
-		return (address != null ? createUrl(address, requestUri) : new URI(requestUri));
+	private static URI initUri(HttpServerRequest request) throws URISyntaxException {
+		Assert.notNull(request, "'request' must not be null");
+		URI baseUri = resolveBaseUrl(request);
+		String requestUri = request.uri();
+		return (baseUri != null ? new URI(baseUri.toString() + requestUri) : new URI(requestUri));
 	}
 
-	private static URI createUrl(InetSocketAddress address, String requestUri) throws URISyntaxException {
-		URI baseUrl = new URI(null, null, address.getHostString(), address.getPort(), null, null, null);
-		return new URI(baseUrl.toString() + requestUri);
+	private static URI resolveBaseUrl(HttpServerRequest request) throws URISyntaxException {
+		String header = request.requestHeaders().get(HttpHeaderNames.HOST);
+		if (header != null) {
+			final int portIndex;
+			if (header.startsWith("[")) {
+				portIndex = header.indexOf(':', header.indexOf(']'));
+			} else {
+				portIndex = header.indexOf(':');
+			}
+			if (portIndex != -1) {
+				try {
+					return new URI(null, null, header.substring(0, portIndex),
+							Integer.parseInt(header.substring(portIndex + 1)), null, null, null);
+				} catch (NumberFormatException ignore) {
+					throw new URISyntaxException(header, "Unable to parse port", portIndex);
+				}
+			}
+			else {
+				return new URI(null, header, null, null);
+			}
+		}
+		else {
+			InetSocketAddress localAddress = (InetSocketAddress) request.context().channel().localAddress();
+			return new URI(null, null, localAddress.getHostString(),
+					localAddress.getPort(), null, null, null);
+		}
 	}
 
 	private static HttpHeaders initHeaders(HttpServerRequest channel) {