diff --git a/artiq/runtime.rs/src/cache.rs b/artiq/runtime.rs/src/cache.rs
index cc755bab6..4136b96f3 100644
--- a/artiq/runtime.rs/src/cache.rs
+++ b/artiq/runtime.rs/src/cache.rs
@@ -44,4 +44,10 @@ impl Cache {
         });
         Ok(())
     }
+
+    pub unsafe fn unborrow(&mut self) {
+        for (_key, entry) in self.entries.iter_mut() {
+            entry.borrowed = false;
+        }
+    }
 }
diff --git a/artiq/runtime.rs/src/session.rs b/artiq/runtime.rs/src/session.rs
index 644381ea8..5b135b226 100644
--- a/artiq/runtime.rs/src/session.rs
+++ b/artiq/runtime.rs/src/session.rs
@@ -381,6 +381,7 @@ fn process_kern_message(waiter: Waiter,
             kern::RunFinished => {
                 kernel::stop();
                 session.kernel_state = KernelState::Absent;
+                unsafe { session.congress.cache.unborrow() }
 
                 match stream {
                     None => return Ok(true),
@@ -392,6 +393,7 @@ fn process_kern_message(waiter: Waiter,
             kern::RunException { exception: ref exn, backtrace } => {
                 kernel::stop();
                 session.kernel_state = KernelState::Absent;
+                unsafe { session.congress.cache.unborrow() }
 
                 match stream {
                     None => {