diff --git a/src/operators/arrange/upsert.rs b/src/operators/arrange/upsert.rs
index 88f137197..b890e4603 100644
--- a/src/operators/arrange/upsert.rs
+++ b/src/operators/arrange/upsert.rs
@@ -193,16 +193,23 @@ where
             let mut priority_queue = BinaryHeap::<std::cmp::Reverse<(G::Timestamp, Tr::Key, Option<Tr::Val>)>>::new();
             let mut updates = Vec::new();
 
+            let mut buffers = Vec::new();
+
             move |input, output| {
 
-                // Stash capabilities and associated data (ordered by time).
+                // Read input out without doing work, to avoid trapping overloaded workers.
                 input.for_each(|cap, data| {
                     capabilities.insert(cap.retain());
                     data.swap(&mut buffer);
-                    for (key, val, time) in buffer.drain(..) {
+                    buffers.push(std::mem::take(&mut buffer));
+                });
+
+                // Stash capabilities and associated data (ordered by time).
+                for buffer in buffers.drain(..) {
+                    for (key, val, time) in buffer {
                         priority_queue.push(std::cmp::Reverse((time, key, val)))
                     }
-                });
+                }
 
                 // Test to see if strict progress has occurred, which happens whenever any element of
                 // the old frontier is not greater or equal to the new frontier. It is only in this