diff --git a/artiq/firmware/runtime/analyzer.rs b/artiq/firmware/runtime/analyzer.rs
index 2e9d74c14..5b090f732 100644
--- a/artiq/firmware/runtime/analyzer.rs
+++ b/artiq/firmware/runtime/analyzer.rs
@@ -79,5 +79,7 @@ pub fn thread(io: Io) {
             Ok(())   => (),
             Err(err) => error!("analyzer aborted: {}", err)
         }
+
+        stream.close().expect("analyzer: close socket")
     }
 }
diff --git a/artiq/firmware/runtime/mgmt.rs b/artiq/firmware/runtime/mgmt.rs
index c100df05f..449ed91be 100644
--- a/artiq/firmware/runtime/mgmt.rs
+++ b/artiq/firmware/runtime/mgmt.rs
@@ -131,6 +131,7 @@ pub fn thread(io: Io) {
                 Err(Error::Io(IoError::UnexpectedEnd)) => (),
                 Err(err) => error!("aborted: {}", err)
             }
+            stream.close().expect("mgmt: close socket");
         });
     }
 }
diff --git a/artiq/firmware/runtime/moninj.rs b/artiq/firmware/runtime/moninj.rs
index 6feb7ec55..36d4bbb47 100644
--- a/artiq/firmware/runtime/moninj.rs
+++ b/artiq/firmware/runtime/moninj.rs
@@ -214,6 +214,7 @@ pub fn thread(io: Io, aux_mutex: &Mutex, routing_table: &Urc<RefCell<drtio_routi
                 Ok(()) => {},
                 Err(err) => error!("moninj aborted: {}", err)
             }
+            stream.close().expect("moninj: close socket");
         });
     }
 }
diff --git a/artiq/firmware/runtime/sched.rs b/artiq/firmware/runtime/sched.rs
index fc3c7ac04..860ec5347 100644
--- a/artiq/firmware/runtime/sched.rs
+++ b/artiq/firmware/runtime/sched.rs
@@ -250,26 +250,14 @@ impl<'a> Io<'a> {
         })
     }
 
-    pub fn inner_until<F: FnMut() -> bool>(
-        &self,
-        timeout: Option<u64>,
-        mut f: F
-    ) -> Result<(), Error> {
+    pub fn until<F: FnMut() -> bool>(&self, mut f: F) -> Result<(), Error> {
         let f = unsafe { mem::transmute::<&mut dyn FnMut() -> bool, *mut dyn FnMut() -> bool>(&mut f) };
         self.suspend(WaitRequest {
-            timeout,
-            event: Some(f),
+            timeout: None,
+            event:   Some(f)
         })
     }
 
-    pub fn until<F: FnMut() -> bool>(&self, f: F) -> Result<(), Error> {
-        self.inner_until(None, f)
-    }
-
-    pub fn until_with_timeout<F: FnMut() -> bool>(&self, timeout: u64, f: F) -> Result<(), Error> {
-        self.inner_until(Some(timeout), f)
-    }
-
     pub fn until_ok<T, E, F>(&self, mut f: F) -> Result<T, Error>
         where F: FnMut() -> result::Result<T, E>
     {
@@ -325,15 +313,7 @@ macro_rules! until {
             let $var = network.get_socket::<$ty>(handle);
             $cond
         })
-    });
-    ($socket:expr, $ty:ty, timeout=$timeout:expr, |$var:ident| $cond:expr) => ({
-        let (network, handle) = ($socket.io.network.clone(), $socket.handle);
-        $socket.io.until_with_timeout($timeout, move || {
-            let mut network = network.borrow_mut();
-            let $var = network.get_socket::<$ty>(handle);
-            $cond
-        })
-    });
+    })
 }
 
 type TcpSocketBuffer = ::smoltcp::socket::TcpSocketBuffer<'static>;
@@ -397,6 +377,10 @@ impl<'a> TcpListener<'a> {
             .map_err(|err| err.into())
     }
 
+    /// Accept a TCP connection
+    ///
+    /// When the returned TcpStream is dropped it is immediately forgotten about. In order to
+    /// ensure that pending data is sent and the far end is notified, `close` must be called.
     pub fn accept(&self) -> Result<TcpStream<'a>, Error> {
         // We're waiting until at least one half of the connection becomes open.
         // This handles the case where a remote socket immediately sends a FIN--
@@ -586,28 +570,20 @@ impl<'a> Write for TcpStream<'a> {
 
 impl<'a> Drop for TcpStream<'a> {
     fn drop(&mut self) {
-        self.with_lower(|s| s.close());
-        let result = until!(
-            self, TcpSocketLower, timeout=clock::get_ms() + 1000, |s| !s.is_active()
+        // There's no point calling the lower close here unless we also defer the removal of the
+        // socket from smoltcp until it's had a chance to process the event
+        let (unsent_bytes, is_open) = self.with_lower(
+            |s| (s.send_queue(), s.is_open())
         );
-        let unsent_bytes = self.with_lower(|s| s.send_queue());
-        match result{
-            Ok(()) => {
-                if unsent_bytes != 0 {
-                    // This is normal if we received a reset whilst sending
-                    debug!("Dropping socket with {} bytes unsent", unsent_bytes)
-                }
-            }
-            Err(Error::TimedOut) => {
-                warn!(
-                    "Timed out whilst waiting for socket to close during drop, with {} unsent bytes",
-                    unsent_bytes
-                );
-            }
-            Err(e) => {
-                error!("Unexpected error whilst waiting for socket to close during drop: {:?}", e)
-            }
+        if is_open {
+            warn!(
+                "Dropping open TcpStream in state {}, with {} unsent bytes",
+                self.with_lower(|s| s.state()), unsent_bytes
+            )
+        } else if unsent_bytes != 0 {
+            debug!("Dropping socket with {} bytes unsent", unsent_bytes)
         }
+
         self.io.network.borrow_mut().remove_socket(self.handle);
     }
 }
diff --git a/artiq/firmware/runtime/session.rs b/artiq/firmware/runtime/session.rs
index aec47afe1..bd1562269 100644
--- a/artiq/firmware/runtime/session.rs
+++ b/artiq/firmware/runtime/session.rs
@@ -650,6 +650,7 @@ pub fn thread(io: Io, aux_mutex: &Mutex,
                         error!("session aborted: {}", err);
                     }
                 }
+                stream.close().expect("session: close socket");
             });
         }