diff --git a/presto-main/src/main/java/io/prestosql/operator/WindowOperator.java b/presto-main/src/main/java/io/prestosql/operator/WindowOperator.java
index 4343974094c56..1796e1c5b0578 100644
--- a/presto-main/src/main/java/io/prestosql/operator/WindowOperator.java
+++ b/presto-main/src/main/java/io/prestosql/operator/WindowOperator.java
@@ -334,6 +334,17 @@ public boolean isFinished()
         return outputPages.isFinished();
     }
 
+    @Override
+    public ListenableFuture<?> isBlocked()
+    {
+        // We can block e.g. because of self-triggered spill
+        if (outputPages.isBlocked()) {
+            return outputPages.getBlockedFuture();
+        }
+
+        return NOT_BLOCKED;
+    }
+
     @Override
     public boolean needsInput()
     {