diff --git a/tools/isobuild/compiler-plugin.js b/tools/isobuild/compiler-plugin.js
index 0b2199518c..cbdaa2431a 100644
--- a/tools/isobuild/compiler-plugin.js
+++ b/tools/isobuild/compiler-plugin.js
@@ -884,12 +884,29 @@ class OutputResource {
     } else if (this._lazyFinalizer) {
       const finalize = this._lazyFinalizer;
       this._lazyFinalizer = null;
-      (this._finalizerPromise = new Promise(
-        resolve => resolve(finalize())
-      ).then(result => {
-        Object.assign(this._initialOptions, result);
-        this._finalizerPromise = null;
-      })).await();
+      (this._finalizerPromise =
+       // It's important to initialize this._finalizerPromise to the new
+       // Promise before calling finalize(), so there's no possibility of
+       // finalize() triggering code that reenters this function before we
+       // have the final version of this._finalizerPromise. If this code
+       // used `new Promise(resolve => resolve(finalize()))` instead of
+       // `Promise.resolve().then(finalize)`, the finalize() call would
+       // begin before this._finalizerPromise was fully initialized.
+       Promise.resolve().then(finalize).then(result => {
+         if (result) {
+           Object.assign(this._initialOptions, result);
+         } else if (this._errors.length === 0) {
+           // In case the finalize() call failed without reporting any
+           // errors, create at least one generic error that can be
+           // reported when reportPendingErrors is called.
+           const error = new Error("lazyFinalizer failed");
+           error.info = { resource: this, finalize }
+           this._errors.push(error);
+         }
+         // The this._finalizerPromise object only survives for the
+         // duration of the initial finalization.
+         this._finalizerPromise = null;
+       })).await();
     }
   }