diff --git a/app/astride/sandbox.js b/app/astride/sandbox.js
index 2c8a9cd..1f4ca19 100644
--- a/app/astride/sandbox.js
+++ b/app/astride/sandbox.js
@@ -704,7 +704,10 @@ export default class Sandbox {
     switch (result.yield) {
       case YIELD_PROMISE: {
         stepResult.async = true;
-        stepResult.value = Promise.resolve(result.value)
+        const promise = result.value instanceof Promise
+          ? result.value
+          : Promise.resolve(result.value);
+        promise
           .then((value) => {
             const top = this.$$execution.stack[this.$$execution.stack.length - 1];
             this.$$execution.deferred.set(top, {
@@ -712,6 +715,7 @@ export default class Sandbox {
               yield: YIELD_NONE,
             });
           });
+        stepResult.value = promise;
         break;
       }
       case YIELD_LOOP_UPDATE: {