diff --git a/src/streaming/pipeline/server.rs b/src/streaming/pipeline/server.rs
index 5a18f267..91548168 100644
--- a/src/streaming/pipeline/server.rs
+++ b/src/streaming/pipeline/server.rs
@@ -131,8 +131,9 @@ impl<P, T, B, S> super::advanced::Dispatch for Dispatch<S, T, P> where
     }
 
     fn poll(&mut self) -> Poll<Option<PipelineMessage<Self::In, Self::Stream, Self::Error>>, io::Error> {
-        for slot in self.in_flight.iter_mut() {
-            slot.poll();
+        match self.in_flight.front_mut() {
+            Some(slot) => slot.poll(),
+            _ => return Ok(Async::NotReady)
         }
 
         match self.in_flight.front() {