diff --git a/demo/client/client.ts b/demo/client/client.ts
index 77020680f..aab723b7e 100644
--- a/demo/client/client.ts
+++ b/demo/client/client.ts
@@ -617,8 +617,12 @@ function addDomListener(element: HTMLElement, type: string, handler: (...args: a
 }
 
 function updateTerminalSize(): void {
+  const showScrollbar = term!.options.scrollbar?.showScrollbar ?? true;
+  const scrollBarWidth = (term!.options.scrollback === 0 || !showScrollbar)
+    ? 0
+    : (term!.options.scrollbar?.width ?? 14);
   const width = optionsWindow.autoResize ? '100%'
-    : ((term as any).dimensions.css.canvas.width + (term as any)._core.viewport.scrollBarWidth).toString() + 'px';
+    : ((term as any).dimensions.css.canvas.width + scrollBarWidth).toString() + 'px';
   const height = optionsWindow.autoResize ? '100%'
     : ((term as any).dimensions.css.canvas.height).toString() + 'px';
   terminalContainer!.style.width = width;
diff --git a/src/browser/Viewport.ts b/src/browser/Viewport.ts
index 115de8d3d..3b6ae8301 100644
--- a/src/browser/Viewport.ts
+++ b/src/browser/Viewport.ts
@@ -27,6 +27,7 @@ export class Viewport extends Disposable {
   private _isSyncing: boolean = false;
   private _isHandlingScroll: boolean = false;
   private _suppressOnScrollHandler: boolean = false;
+  private _needsSyncOnRender: boolean = false;
 
   constructor(
     element: HTMLElement,
@@ -105,6 +106,16 @@ export class Viewport extends Disposable {
     }));
     this._register(this._bufferService.onScroll(() => this._sync()));
 
+    // Flush deferred viewport sync after a render completes (e.g. after ESU ends
+    // synchronized output mode). This ensures DOM scroll position updates atomically
+    // with the canvas render.
+    this._register(this._renderService.onRender(() => {
+      if (this._needsSyncOnRender) {
+        this._needsSyncOnRender = false;
+        this._sync();
+      }
+    }));
+
     this._register(this._scrollableElement.onScroll(e => this._handleScroll(e)));
 
   }
@@ -162,8 +173,12 @@ export class Viewport extends Disposable {
     if (!this._renderService || this._isSyncing) {
       return;
     }
-    // Plumb synchronized output state into Viewport for follow-up behavior changes.
-    void this._coreService.decPrivateModes.synchronizedOutput;
+    // Defer DOM scroll updates during synchronized output to prevent visible
+    // scroll position flickering while the canvas content is frozen.
+    if (this._coreService.decPrivateModes.synchronizedOutput) {
+      this._needsSyncOnRender = true;
+      return;
+    }
     this._isSyncing = true;
 
     // Ignore any onScroll event that happens as a result of dimensions changing as this should