diff --git a/gerrit-sshd/src/main/java/com/google/gerrit/sshd/commands/ScpCommand.java b/gerrit-sshd/src/main/java/com/google/gerrit/sshd/commands/ScpCommand.java
index 09c25ff..987380f 100644
--- a/gerrit-sshd/src/main/java/com/google/gerrit/sshd/commands/ScpCommand.java
+++ b/gerrit-sshd/src/main/java/com/google/gerrit/sshd/commands/ScpCommand.java
@@ -92,6 +92,7 @@
 
   private void runImp() {
     try {
+      readAck();
       if (error != null) {
         throw error;
       }