diff --git a/xds/src/main/java/io/grpc/xds/ExternalProcessorClientInterceptor.java b/xds/src/main/java/io/grpc/xds/ExternalProcessorClientInterceptor.java
index f61e1002926..2b56ed1b8ec 100644
--- a/xds/src/main/java/io/grpc/xds/ExternalProcessorClientInterceptor.java
+++ b/xds/src/main/java/io/grpc/xds/ExternalProcessorClientInterceptor.java
@@ -851,6 +851,11 @@ public void halfClose() {
       pendingHalfClose.set(true);
 
       if (extProcStreamState.get().isCompleted()) {
+        if (passThroughMode.get()) {
+          if (requestSideClosed.compareAndSet(false, true)) {
+            proceedWithHalfClose();
+          }
+        }
         return;
       }