diff --git a/apps/web/src/pages/ReaderPage.tsx b/apps/web/src/pages/ReaderPage.tsx
index f4b46e3..ab4cb54 100644
--- a/apps/web/src/pages/ReaderPage.tsx
+++ b/apps/web/src/pages/ReaderPage.tsx
@@ -162,7 +162,7 @@ export function ReaderPage({ bookId }: { bookId: number }) {
   const changeZoom = useCallback((nextZoom: number | ((currentZoom: number) => number)) => {
     const stage = document.querySelector(".reader-stage") as HTMLElement | null;
     const scrollRatioX = stage && stage.scrollWidth > stage.clientWidth ? (stage.scrollLeft + stage.clientWidth / 2) / stage.scrollWidth : 0.5;
-    const scrollRatioY = stage && stage.scrollHeight > stage.clientHeight ? (stage.scrollTop + stage.clientHeight / 2) / stage.scrollHeight : 0.5;
+    const scrollRatioY = stage && stage.scrollHeight > stage.clientHeight ? stage.scrollTop / (stage.scrollHeight - stage.clientHeight) : 0;
 
     setZoom((currentZoom) => clampReaderZoom(typeof nextZoom === "function" ? nextZoom(currentZoom) : nextZoom));
 
@@ -170,7 +170,7 @@ export function ReaderPage({ bookId }: { bookId: number }) {
       requestAnimationFrame(() => {
         if (!stage) return;
         stage.scrollLeft = Math.max(0, stage.scrollWidth * scrollRatioX - stage.clientWidth / 2);
-        stage.scrollTop = Math.max(0, stage.scrollHeight * scrollRatioY - stage.clientHeight / 2);
+        stage.scrollTop = Math.max(0, (stage.scrollHeight - stage.clientHeight) * scrollRatioY);
       });
     });
   }, []);
diff --git a/apps/web/src/pages/ReaderPageVerticalRestore.test.ts b/apps/web/src/pages/ReaderPageVerticalRestore.test.ts
index 39bb1ea..d533831 100644
--- a/apps/web/src/pages/ReaderPageVerticalRestore.test.ts
+++ b/apps/web/src/pages/ReaderPageVerticalRestore.test.ts
@@ -8,4 +8,12 @@ describe("ReaderPage vertical restore", () => {
 
     expect(bookResetEffect).toContain("setPage(1)");
   });
+
+  it("does not restore an unknown vertical scroll anchor to the middle of the book", () => {
+    const source = readFileSync(new URL("./ReaderPage.tsx", import.meta.url), "utf8");
+    const changeZoomBlock = source.slice(source.indexOf("const changeZoom = useCallback"), source.indexOf("  const zoomControls", source.indexOf("const changeZoom = useCallback")));
+
+    expect(changeZoomBlock).toContain("scrollRatioY");
+    expect(changeZoomBlock).not.toMatch(/scrollRatioY[\s\S]*:\s*0\.5/);
+  });
 });