diff --git a/timely/src/dataflow/operators/core/probe.rs b/timely/src/dataflow/operators/core/probe.rs
index b6035ae13..0abac98ed 100644
--- a/timely/src/dataflow/operators/core/probe.rs
+++ b/timely/src/dataflow/operators/core/probe.rs
@@ -94,6 +94,8 @@ impl<G: Scope, C: Container> Probe<G, C> for StreamCore<G, C> {
         let (tee, stream) = builder.new_output();
         let mut output = PushBuffer::new(PushCounter::new(tee));
 
+        handle.frontier.borrow_mut().update_iter(std::iter::once((Timestamp::minimum(), 1)));
+
         let shared_frontier = Rc::downgrade(&handle.frontier);
         let mut started = false;
 
@@ -111,6 +113,10 @@ impl<G: Scope, C: Container> Probe<G, C> for StreamCore<G, C> {
                 if !started {
                     // discard initial capability.
                     progress.internals[0].update(G::Timestamp::minimum(), -1);
+                    if let Some(shared_frontier) = shared_frontier.upgrade() {
+                        let mut borrow = shared_frontier.borrow_mut();
+                        borrow.update_iter(std::iter::once((Timestamp::minimum(), -1)));
+                    }
                     started = true;
                 }
 
diff --git a/timely/src/dataflow/operators/generic/builder_raw.rs b/timely/src/dataflow/operators/generic/builder_raw.rs
index 8ba131612..59689b432 100644
--- a/timely/src/dataflow/operators/generic/builder_raw.rs
+++ b/timely/src/dataflow/operators/generic/builder_raw.rs
@@ -228,11 +228,5 @@ where
         (self.summary.clone(), self.shared_progress.clone())
     }
 
-    // initialize self.frontier antichains as indicated by hosting scope.
-    fn set_external_summary(&mut self) {
-        // should we schedule the operator here, or just await the first invocation?
-        self.schedule();
-    }
-
     fn notify_me(&self) -> bool { self.shape.notify }
 }
diff --git a/timely/src/progress/operate.rs b/timely/src/progress/operate.rs
index 28fd10ae8..c671533f5 100644
--- a/timely/src/progress/operate.rs
+++ b/timely/src/progress/operate.rs
@@ -46,14 +46,6 @@ pub trait Operate<T: Timestamp> : Schedule {
     /// any output, and no initial capabilities are held.
     fn get_internal_summary(&mut self) -> (Vec<Vec<Antichain<T::Summary>>>, Rc<RefCell<SharedProgress<T>>>);
 
-    /// Signals that external frontiers have been set.
-    ///
-    /// By default this method does nothing, and leaves all changes in the `frontiers` element
-    /// of the shared progress state. An operator should be able to consult `frontiers` at any
-    /// point and read out the current frontier information, or the changes from the last time
-    /// that `frontiers` was drained.
-    fn set_external_summary(&mut self) { }
-
     /// Indicates of whether the operator requires `push_external_progress` information or not.
     fn notify_me(&self) -> bool { true }
 }
diff --git a/timely/src/progress/subgraph.rs b/timely/src/progress/subgraph.rs
index dbe735655..8f0966034 100644
--- a/timely/src/progress/subgraph.rs
+++ b/timely/src/progress/subgraph.rs
@@ -581,15 +581,6 @@ where
         // Return summaries and shared progress information.
         (internal_summary, self.shared_progress.clone())
     }
-
-    fn set_external_summary(&mut self) {
-        self.accept_frontier();
-        self.propagate_pointstamps();  // ensure propagation of input frontiers.
-        self.children
-            .iter_mut()
-            .flat_map(|child| child.operator.as_mut())
-            .for_each(|op| op.set_external_summary());
-    }
 }
 
 struct PerOperatorState<T: Timestamp> {
diff --git a/timely/src/worker.rs b/timely/src/worker.rs
index 4a5c0145b..523fc615f 100644
--- a/timely/src/worker.rs
+++ b/timely/src/worker.rs
@@ -652,7 +652,6 @@ impl<A: Allocate> Worker<A> {
         }
 
         operator.get_internal_summary();
-        operator.set_external_summary();
 
         let mut temp_channel_ids = self.temp_channel_ids.borrow_mut();
         let channel_ids = temp_channel_ids.drain(..).collect::<Vec<_>>();