diff --git a/build.gradle b/build.gradle
index 8de3f484c4..0a1cc7d2c8 100644
--- a/build.gradle
+++ b/build.gradle
@@ -47,7 +47,7 @@ configure(allprojects) { project ->
 			mavenBom "io.netty:netty-bom:4.1.39.Final"
 			mavenBom "io.projectreactor:reactor-bom:Dysprosium-RELEASE"
 			mavenBom "io.rsocket:rsocket-bom:1.0.0-RC5"
-			mavenBom "org.eclipse.jetty:jetty-bom:9.4.20.v20190813"
+			mavenBom "org.eclipse.jetty:jetty-bom:9.4.21.v20190926"
 			mavenBom "org.jetbrains.kotlin:kotlin-bom:1.3.50"
 			mavenBom "org.jetbrains.kotlinx:kotlinx-coroutines-bom:1.3.2"
 			mavenBom "org.junit:junit-bom:5.5.2"
diff --git a/spring-websocket/src/main/java/org/springframework/web/socket/server/jetty/JettyRequestUpgradeStrategy.java b/spring-websocket/src/main/java/org/springframework/web/socket/server/jetty/JettyRequestUpgradeStrategy.java
index fab7634b9f..b3a10faf88 100644
--- a/spring-websocket/src/main/java/org/springframework/web/socket/server/jetty/JettyRequestUpgradeStrategy.java
+++ b/spring-websocket/src/main/java/org/springframework/web/socket/server/jetty/JettyRequestUpgradeStrategy.java
@@ -30,7 +30,6 @@ import javax.servlet.http.HttpServletResponse;
 
 import org.eclipse.jetty.websocket.api.WebSocketPolicy;
 import org.eclipse.jetty.websocket.api.extensions.ExtensionConfig;
-import org.eclipse.jetty.websocket.api.extensions.ExtensionFactory;
 import org.eclipse.jetty.websocket.server.HandshakeRFC6455;
 import org.eclipse.jetty.websocket.server.WebSocketServerFactory;
 
@@ -180,14 +179,17 @@ public class JettyRequestUpgradeStrategy implements RequestUpgradeStrategy, Serv
 		return result;
 	}
 
-	@SuppressWarnings({"unchecked"})
+	@SuppressWarnings({"unchecked", "deprecation"})
 	private Set<String> getExtensionNames() {
 		try {
-			return this.factory.getExtensionFactory().getExtensionNames();
+			return this.factory.getAvailableExtensionNames();
 		}
 		catch (IncompatibleClassChangeError ex) {
+			// Fallback for versions prior to 9.4.21:
 			// 9.4.20.v20190813: ExtensionFactory (abstract class -> interface)
-			Method method = ClassUtils.getMethod(ExtensionFactory.class, "getExtensionNames");
+			// 9.4.21.v20190926: ExtensionFactory (interface -> abstract class) + deprecated
+			Class<?> clazz = org.eclipse.jetty.websocket.api.extensions.ExtensionFactory.class;
+			Method method = ClassUtils.getMethod(clazz, "getExtensionNames");
 			return (Set<String>) ReflectionUtils.invokeMethod(method, this.factory.getExtensionFactory());
 		}
 	}