diff --git a/routers/exam/templates.py b/routers/exam/templates.py
index 953797f..ae7b2f9 100644
--- a/routers/exam/templates.py
+++ b/routers/exam/templates.py
@@ -13,6 +13,7 @@ join keys (spec §2).
 from __future__ import annotations
 
 import json
+import math
 import os
 import tempfile
 import time
@@ -369,7 +370,10 @@ def _pdf_page_geometry(pdf_bytes: bytes) -> List[Dict[str, float]]:
                 # pages by those heights. Previously rendered_w/h were left in PDF points (~595x842),
                 # so every shape landed shrunk (~0.76x) and shifted up-left on the 780-wide canvas.
                 rendered_w = CANVAS_PAGE_WIDTH
-                rendered_h = CANVAS_PAGE_WIDTH * page_pt_h / page_pt_w
+                # Mirror the app's canvas.height = Math.ceil(viewport.height) EXACTLY (pdfLoader.ts),
+                # so page_top accumulates identically. Using the raw float drifts ~1px/page, compounding
+                # to a visible upward shift on later pages of long papers (~36px over 40 pages).
+                rendered_h = float(math.ceil(CANVAS_PAGE_WIDTH * page_pt_h / page_pt_w))
                 pages.append({
                     "media_x0": float(media.x0),
                     "crop_x0": float(crop.x0),
@@ -397,7 +401,7 @@ def _pdf_page_geometry(pdf_bytes: bytes) -> List[Dict[str, float]]:
 def _page_geom(pages: List[Dict[str, float]], page_number: int) -> Dict[str, float]:
     if 1 <= page_number <= len(pages):
         return pages[page_number - 1]
-    _fallback_h = CANVAS_PAGE_WIDTH * 842.0 / 595.0
+    _fallback_h = float(math.ceil(CANVAS_PAGE_WIDTH * 842.0 / 595.0))
     return {
         "media_x0": 0.0, "crop_x0": 0.0, "crop_y0": 0.0,
         "page_pt_w": 595.0, "page_pt_h": 842.0,