diff --git a/src/pyj/read_book/view.pyj b/src/pyj/read_book/view.pyj
index a4ad375666..af331508dc 100644
--- a/src/pyj/read_book/view.pyj
+++ b/src/pyj/read_book/view.pyj
@@ -163,7 +163,9 @@ def show_controls_help():
 
 def body_font_size():
     ans = body_font_size.ans
-    if not ans:
+    dpr = body_font_size.dpr
+    if not ans or window.devicePixelRatio is not dpr:
+        body_font_size.dpr = window.devicePixelRatio
         q = window.getComputedStyle(document.body).fontSize
         if q and q.endsWith('px'):
             q = parseInt(q)