diff --git a/requestfactory/build.xml b/requestfactory/build.xml
index c835c86da4..543a373463 100755
--- a/requestfactory/build.xml
+++ b/requestfactory/build.xml
@@ -45,6 +45,7 @@
         <jvmarg value="-ea"/>
         <arg value="@{target}"/>
         <arg file="${gwt.build.lib}/requestfactory-@{target}.jar"/>
+        <arg value="used-to-build-gwt" />
       </java>
     </sequential>
   </macrodef>
diff --git a/user/src/com/google/web/bindery/requestfactory/server/RequestFactoryJarExtractor.java b/user/src/com/google/web/bindery/requestfactory/server/RequestFactoryJarExtractor.java
index daeb5a2fde..a8c807e296 100644
--- a/user/src/com/google/web/bindery/requestfactory/server/RequestFactoryJarExtractor.java
+++ b/user/src/com/google/web/bindery/requestfactory/server/RequestFactoryJarExtractor.java
@@ -98,7 +98,11 @@
 
 /**
  * Used to extract RequestFactory client jars from {@code gwt-user.jar}.
+ *
+ * @deprecated Will not be deleted from source, but will no longer be included in GWT artifacts, as
+ * this is only intended for use as a build tool.
  */
+@Deprecated
 public class RequestFactoryJarExtractor {
   /*
    * The FooProcessor types are ASM visitors that traverse the bytecode, calling
@@ -843,6 +847,12 @@ public static void main(String[] args) throws IOException {
       }
       System.exit(1);
     }
+    if (args.length != 3 || !"used-to-build-gwt".equals(args[2])) {
+      // Test for magic sentinel, warn if not present
+      System.err.println("RequestFactoryJarExtractor is deprecated for removal from build " +
+              "artifacts, if you have a use case that requires it please discuss at " +
+              "https://github.com/gwtproject/gwt/issues/9923.");
+    }
     String target = args[0];
     List<Class<?>> seeds = SEEDS.get(target);
     if (seeds == null) {