diff --git a/xds/src/test/java/io/grpc/xds/ExternalProcessorClientInterceptorTest.java b/xds/src/test/java/io/grpc/xds/ExternalProcessorClientInterceptorTest.java
index 2f7387c1f12..2e8761214a3 100644
--- a/xds/src/test/java/io/grpc/xds/ExternalProcessorClientInterceptorTest.java
+++ b/xds/src/test/java/io/grpc/xds/ExternalProcessorClientInterceptorTest.java
@@ -14309,9 +14309,15 @@ public StreamObserver<ProcessingRequest> process(
             return new StreamObserver<ProcessingRequest>() {
               @Override
               public void onNext(ProcessingRequest request) {
-                responseObserver.onNext(ProcessingResponse.newBuilder()
-                    .setRequestHeaders(HeadersResponse.newBuilder().build())
-                    .build());
+                if (request.hasRequestHeaders()) {
+                  responseObserver.onNext(ProcessingResponse.newBuilder()
+                      .setRequestHeaders(HeadersResponse.newBuilder().build())
+                      .build());
+                } else if (request.hasResponseHeaders()) {
+                  responseObserver.onNext(ProcessingResponse.newBuilder()
+                      .setResponseHeaders(HeadersResponse.newBuilder().build())
+                      .build());
+                }
               }
 
               @Override