diff --git a/datafusion/physical-plan/src/sorts/merge.rs b/datafusion/physical-plan/src/sorts/merge.rs
index 01b19f618f8e4..4a7928efe504d 100644
--- a/datafusion/physical-plan/src/sorts/merge.rs
+++ b/datafusion/physical-plan/src/sorts/merge.rs
@@ -171,11 +171,16 @@ impl<C: CursorValues> SortPreservingMergeStream<C> {
             // Ensure all non-exhausted streams have a cursor from which
             // rows can be pulled
             loop {
-                for i in 0..self.streams.partitions() {
+                let uninitiated_cursors = self.uninitiated_cursors.clone();
+                for i in uninitiated_cursors {
                     if self.uninitiated_cursors.contains(&i) {
-                        if let Poll::Ready(Err(e)) = self.maybe_poll_stream(cx, i) {
-                            self.aborted = true;
-                            return Poll::Ready(Some(Err(e)));
+                        match self.maybe_poll_stream(cx, i) {
+                            Poll::Ready(Err(e)) => {
+                                self.aborted = true;
+                                return Poll::Ready(Some(Err(e)));
+                            }
+                            Poll::Pending => return Poll::Pending,
+                            _ => {}
                         }
                     }
                 }