diff --git a/app/node/output/viewer/viewer.cpp b/app/node/output/viewer/viewer.cpp
index 577c7d15d..169de22cc 100644
--- a/app/node/output/viewer/viewer.cpp
+++ b/app/node/output/viewer/viewer.cpp
@@ -200,6 +200,10 @@ void ViewerOutput::UpdateTrackCache()
 
 void ViewerOutput::VerifyLength()
 {
+  if (operation_stack_ != 0) {
+    return;
+  }
+
   NodeTraverser traverser;
 
   rational video_length;