diff --git a/sql/core/src/main/scala/org/apache/spark/sql/execution/python/ArrowPythonRunner.scala b/sql/core/src/main/scala/org/apache/spark/sql/execution/python/ArrowPythonRunner.scala
index 98738bf5c06cf..c1c746fb3bdcc 100644
--- a/sql/core/src/main/scala/org/apache/spark/sql/execution/python/ArrowPythonRunner.scala
+++ b/sql/core/src/main/scala/org/apache/spark/sql/execution/python/ArrowPythonRunner.scala
@@ -157,6 +157,7 @@ class ArrowPythonRunner(
               batch.setNumRows(root.getRowCount)
               batch
             } else {
+              // Reach end of stream. Call `read()` again to read control data.
               read()
             }
           } else {