diff --git a/spec/api-debugger.spec.ts b/spec/api-debugger.spec.ts
index a3f17794ee..5e92c7718f 100644
--- a/spec/api-debugger.spec.ts
+++ b/spec/api-debugger.spec.ts
@@ -235,27 +235,28 @@ describe('debugger module', () => {
     });
 
     it('does not crash for invalid unicode characters in message', async () => {
-      w.webContents.debugger.attach();
-
-      const loadingFinished = new Promise<void>((resolve) => {
-        w.webContents.debugger.on('message', (event, method) => {
-          // loadingFinished indicates that page has been loaded and it did not
-          // crash because of invalid UTF-8 data
-          if (method === 'Network.loadingFinished') {
-            resolve();
-          }
-        });
-      });
-
       server = http.createServer((req, res) => {
         res.setHeader('Content-Type', 'text/plain; charset=utf-8');
         res.end('\uFFFF');
       });
 
       const { url } = await listen(server);
-      w.webContents.debugger.sendCommand('Network.enable');
-      w.loadURL(url);
+      // Network.enable only reaches the renderer once it exists. On a fresh
+      // window that is during the first navigation, which can then finish
+      // before the renderer reports Network.loadingFinished. Load a page
+      // first and wait for Network.enable before the real navigation.
+      await w.loadURL('about:blank');
+      w.webContents.debugger.attach();
+      await w.webContents.debugger.sendCommand('Network.enable');
 
+      // loadingFinished indicates that page has been loaded and it did not
+      // crash because of invalid UTF-8 data
+      const loadingFinished = emittedUntil(
+        w.webContents.debugger,
+        'message',
+        (_event: any, method: string) => method === 'Network.loadingFinished'
+      );
+      await w.loadURL(url);
       await loadingFinished;
     });
 
diff --git a/spec/fixtures/pages/beforeunload-false.html b/spec/fixtures/pages/beforeunload-false.html
index 0b71b07c83..6626f38a31 100644
--- a/spec/fixtures/pages/beforeunload-false.html
+++ b/spec/fixtures/pages/beforeunload-false.html
@@ -2,10 +2,11 @@
 <body>
 <script type="text/javascript" charset="utf-8">
   window.onbeforeunload = function() {
-    setTimeout(function() {
-        var ipcRenderer = require('electron').ipcRenderer;
-      ipcRenderer.sendToHost('onbeforeunload');
-    }, 0);
+    // Report synchronously. Without a user gesture Chromium skips the
+    // confirmation and the navigation goes ahead, so a deferred message can
+    // be dropped when this document unloads.
+    var ipcRenderer = require('electron').ipcRenderer;
+    ipcRenderer.sendToHost('onbeforeunload');
     return false;
   }
 </script>
diff --git a/spec/webview.spec.ts b/spec/webview.spec.ts
index 383c10d186..1929232a9d 100644
--- a/spec/webview.spec.ts
+++ b/spec/webview.spec.ts
@@ -230,37 +230,48 @@ describe('<webview> tag', () => {
     });
   });
 
-  ifdescribe(process.platform !== 'win32')('document.visibilityState/hidden', () => {
+  // The guest's visibility follows whether the embedder window is actually on
+  // screen, so this needs the screen to itself (see the BrowserWindow
+  // visibilityState specs): on macOS a window from another spec worker can
+  // occlude this one and hide the guest.
+  ifdescribe(process.platform !== 'win32')('document.visibilityState/hidden', { tags: ['serial'] }, () => {
     afterEach(() => {
       ipcMain.removeAllListeners('pong');
     });
 
     afterEach(closeAllWindows);
 
+    // The guest reports its state when its script runs and on every
+    // visibilitychange. Wait for the expected state rather than taking the
+    // next report: the guest can run its script while it is still being
+    // attached, before the embedder has shown it, and report 'hidden' first.
+    const guestVisibility = (state: 'visible' | 'hidden') =>
+      emittedUntil(ipcMain, 'pong', (_event: unknown, visibilityState: string) => visibilityState === state);
+
     it('follows the embedder window when it is hidden and shown again', async () => {
       const w = new BrowserWindow({
         width: 100,
         height: 100,
         webPreferences: { webviewTag: true, nodeIntegration: true, contextIsolation: false }
       });
+      const initiallyVisible = guestVisibility('visible');
       w.loadFile(path.join(fixtures, 'pages', 'webview-visibilitychange.html'));
       {
-        const [, visibilityState, hidden] = await once(ipcMain, 'pong');
-        expect(visibilityState).toBe('visible');
+        const [, , hidden] = await initiallyVisible;
         expect(hidden).toBe(false);
       }
 
+      const hiddenState = guestVisibility('hidden');
       w.hide();
       {
-        const [, visibilityState, hidden] = await once(ipcMain, 'pong');
-        expect(visibilityState).toBe('hidden');
+        const [, , hidden] = await hiddenState;
         expect(hidden).toBe(true);
       }
 
+      const visibleState = guestVisibility('visible');
       w.show();
       {
-        const [, visibilityState, hidden] = await once(ipcMain, 'pong');
-        expect(visibilityState).toBe('visible');
+        const [, , hidden] = await visibleState;
         expect(hidden).toBe(false);
       }
     });