diff --git a/test/integration/scripting_spec.js b/test/integration/scripting_spec.js
index bde715249..43fc949d1 100644
--- a/test/integration/scripting_spec.js
+++ b/test/integration/scripting_spec.js
@@ -30,9 +30,12 @@ describe("Interaction", () => {
     it("must check that first text field has focus", async () => {
       await Promise.all(
         pages.map(async ([browserName, page]) => {
+          await page.waitForFunction(
+            "window.PDFViewerApplication.scriptingReady === true"
+          );
+
           // The document has an open action in order to give
           // the focus to 401R.
-          await page.waitForTimeout(1000);
           const id = await page.evaluate(
             () => window.document.activeElement.id
           );
diff --git a/web/app.js b/web/app.js
index 4623b3632..67f558778 100644
--- a/web/app.js
+++ b/web/app.js
@@ -1480,7 +1480,12 @@ const PDFViewerApplication = {
     // of the sandbox and removal of the event listeners at document closing.
     const internalEvents = new Map(),
       domEvents = new Map();
-    this._scriptingInstance = { scripting, internalEvents, domEvents };
+    this._scriptingInstance = {
+      scripting,
+      ready: false,
+      internalEvents,
+      domEvents,
+    };
 
     if (!this.documentInfo) {
       // It should be *extremely* rare for metadata to not have been resolved
@@ -1612,6 +1617,15 @@ const PDFViewerApplication = {
       id: "doc",
       name: "Open",
     });
+
+    // Used together with the integration-tests, see the `scriptingReady`
+    // getter, to enable awaiting full initialization of the scripting/sandbox.
+    // (Defer this slightly, to make absolutely sure that everything is done.)
+    Promise.resolve().then(() => {
+      if (this._scriptingInstance) {
+        this._scriptingInstance.ready = true;
+      }
+    });
   },
 
   /**
@@ -2242,6 +2256,14 @@ const PDFViewerApplication = {
     this._wheelUnusedTicks -= wholeTicks;
     return wholeTicks;
   },
+
+  /**
+   * Used together with the integration-tests, to enable awaiting full
+   * initialization of the scripting/sandbox.
+   */
+  get scriptingReady() {
+    return this._scriptingInstance?.ready || false;
+  },
 };
 
 let validateFileURL;