diff --git a/src/main/java/com/googlesource/gerrit/plugins/lfs/LfsSshAuth.java b/src/main/java/com/googlesource/gerrit/plugins/lfs/LfsSshAuth.java
index 61a6032..08d7ca7 100644
--- a/src/main/java/com/googlesource/gerrit/plugins/lfs/LfsSshAuth.java
+++ b/src/main/java/com/googlesource/gerrit/plugins/lfs/LfsSshAuth.java
@@ -48,6 +48,9 @@
 
   @Override
   public String authenticate(CurrentUser user, List<String> args) throws UnloggedFailure, Failure {
+    if (args.size() != 2) {
+      throw new UnloggedFailure(1, "Unexpected number of arguments");
+    }
     try {
       URL url = new URL(canonicalWebUrl);
       String path = url.getPath();