diff --git a/web/pdf_viewer.mjs b/web/pdf_viewer.mjs
--- a/web/pdf_viewer.mjs
+++ b/web/pdf_viewer.mjs
@@ -5192,11 +5192,11 @@
     if (visibleArea.minX < minDetailX || visibleArea.minY < minDetailY || visibleArea.maxX > maxDetailX || visibleArea.maxY > maxDetailY) {
       return true;
     }
+    const { scale } = this.pageView.viewport;
     const {
-      width: maxWidth,
-      height: maxHeight,
-      scale
-    } = this.pageView.viewport;
+      clientWidth: maxWidth,
+      clientHeight: maxHeight
+    } = this.pageView._ensureCanvasWrapper();
     if (this.#detailArea.scale !== scale) {
       return true;
     }
@@ -5237,12 +5237,15 @@
     if (overflowScale < 0) {
       overflowScale = 0;
     }
+    const canvasWrapper = this.pageView._ensureCanvasWrapper();
+    const { pixelRatio } = OutputScale;
     const overflowWidth = visibleWidth * overflowScale;
     const overflowHeight = visibleHeight * overflowScale;
-    const minX = Math.max(0, visibleArea.minX - overflowWidth);
-    const maxX = Math.min(viewport.width, visibleArea.maxX + overflowWidth);
-    const minY = Math.max(0, visibleArea.minY - overflowHeight);
-    const maxY = Math.min(viewport.height, visibleArea.maxY + overflowHeight);
+    // Visible bounds and tile coverage share the rounded page's device pixels.
+    const minX = Math.floor(Math.max(0, visibleArea.minX - overflowWidth) * pixelRatio) / pixelRatio;
+    const maxX = Math.ceil(Math.min(canvasWrapper.clientWidth, visibleArea.maxX + overflowWidth) * pixelRatio) / pixelRatio;
+    const minY = Math.floor(Math.max(0, visibleArea.minY - overflowHeight) * pixelRatio) / pixelRatio;
+    const maxY = Math.ceil(Math.min(canvasWrapper.clientHeight, visibleArea.maxY + overflowHeight) * pixelRatio) / pixelRatio;
     const width = maxX - minX;
     const height = maxY - minY;
     this.#detailArea = {
@@ -5263,11 +5266,9 @@
       return baseContext;
     }
     const {
-      viewport: {
-        width: vWidth,
-        height: vHeight
-      }
-    } = this.pageView;
+      clientWidth: vWidth,
+      clientHeight: vHeight
+    } = this.pageView._ensureCanvasWrapper();
     const {
       width: aWidth,
       height: aHeight,
@@ -5330,16 +5331,22 @@
     const {
       pixelRatio
     } = OutputScale;
-    const transform = [pixelRatio, 0, 0, pixelRatio, -area.minX * pixelRatio, -area.minY * pixelRatio];
-    canvas.width = area.width * pixelRatio;
-    canvas.height = area.height * pixelRatio;
+    const pageWidth = canvasWrapper.clientWidth;
+    const pageHeight = canvasWrapper.clientHeight;
+    const scaleX = pageWidth * pixelRatio / width;
+    const scaleY = pageHeight * pixelRatio / height;
+    const left = Math.round(area.minX * pixelRatio);
+    const top = Math.round(area.minY * pixelRatio);
+    const transform = [scaleX, 0, 0, scaleY, -left, -top];
+    canvas.width = Math.round(area.width * pixelRatio);
+    canvas.height = Math.round(area.height * pixelRatio);
     const {
       style
     } = canvas;
-    style.width = `${area.width * 100 / width}%`;
-    style.height = `${area.height * 100 / height}%`;
-    style.top = `${area.minY * 100 / height}%`;
-    style.left = `${area.minX * 100 / width}%`;
+    style.width = `${canvas.width * 100 / (pageWidth * pixelRatio)}%`;
+    style.height = `${canvas.height * 100 / (pageHeight * pixelRatio)}%`;
+    style.top = `${top * 100 / (pageHeight * pixelRatio)}%`;
+    style.left = `${left * 100 / (pageWidth * pixelRatio)}%`;
     const renderingPromise = this._drawCanvas(this._getRenderingContext(canvas, transform), () => {
       this.canvas?.remove();
       this.canvas = prevCanvas;