diff --git a/oden-js/src/runtime.rs b/oden-js/src/runtime.rs
index 1719f3a0..e349d955 100644
--- a/oden-js/src/runtime.rs
+++ b/oden-js/src/runtime.rs
@@ -175,37 +175,44 @@ impl Runtime {
 
     /// Process all pending async jobs. This includes all promise resolutions.
     fn process_promise_completions(&self) {
-        // TODO: This could be more robust if we buffered all the completed
-        //       promise entries and then dropped the borrow of the state, so
-        //       that we never invoked user code while borrowing our private
-        //       state mutably.
+        let mut promises = vec![];
+
+        // First, gather all the completed promises into a temporary vector
+        // so that we only need to borrow our mutable state for a short
+        // period of time.
         let mut state = unsafe { PrivateState::from_rt_mut(self.rt) };
         while let Ok((handle, evt)) = state.promise_recv.try_recv() {
             if let Some(entry) = state.promise_table.remove(&handle) {
-                let ctx = ContextRef::from_raw(entry.context);
-                let (callback, value) = match evt {
-                    PromiseEvent::Resolved(v) => (entry.resolve, v),
-                    PromiseEvent::Rejected(v) => (entry.reject, v),
-                };
-
-                // Convert the result into a JS value, which we can only
-                // really do while we are on this thread.
-                let value = value(&ctx).expect("Should be able to convert promise result to value");
-
-                // Call the particular callback and make sure it doesn't throw.
-                ctx.check_exception(unsafe {
-                    let mut args = [value.val];
-                    sys::JS_Call(
-                        entry.context,
-                        callback,
-                        sys::JS_MakeUndefined(),
-                        1,
-                        args.as_mut_ptr(),
-                    )
-                })
-                .expect("Exception thrown by promise callback");
+                promises.push((entry, evt));
             }
         }
+        drop(state); // Don't need our internal state anymore.
+
+        // Nowe we can complete all the promises.
+        for (entry, evt) in promises {
+            let ctx = ContextRef::from_raw(entry.context);
+            let (callback, value) = match evt {
+                PromiseEvent::Resolved(v) => (entry.resolve, v),
+                PromiseEvent::Rejected(v) => (entry.reject, v),
+            };
+
+            // Convert the result into a JS value, which we can only
+            // really do while we are on this thread.
+            let value = value(&ctx).expect("Should be able to convert promise result to value");
+
+            // Call the particular callback and make sure it doesn't throw.
+            ctx.check_exception(unsafe {
+                let mut args = [value.val];
+                sys::JS_Call(
+                    entry.context,
+                    callback,
+                    sys::JS_MakeUndefined(),
+                    1,
+                    args.as_mut_ptr(),
+                )
+            })
+            .expect("Exception thrown by promise callback");
+        }
     }
 
     /// Process all pending async jobs. This includes all promise resolutions.