diff --git a/src/pyj/read_book/paged_mode.pyj b/src/pyj/read_book/paged_mode.pyj
index 9db51a3ba5..3b417a6b2e 100644
--- a/src/pyj/read_book/paged_mode.pyj
+++ b/src/pyj/read_book/paged_mode.pyj
@@ -152,18 +152,21 @@ def cps_by_em_size():
     ans = cps_by_em_size.ans
     fs = window.getComputedStyle(document.body).fontSize
     if not ans or cps_by_em_size.at_font_size is not fs:
-        d = document.createElement('span')
-        d.style.position = 'absolute'
-        d.style.visibility = 'hidden'
-        d.style.width = '1rem'
-        d.style.fontSize = '1rem'
-        d.style.paddingTop = d.style.paddingBottom = d.style.paddingLeft = d.style.paddingRight = '0'
-        d.style.marginTop = d.style.marginBottom = d.style.marginLeft = d.style.marginRight = '0'
-        d.style.borderStyle = 'none'
-        document.body.appendChild(d)
-        w = d.clientWidth
-        document.body.removeChild(d)
-        ans = cps_by_em_size.ans = max(2, w)
+        if fs is 0:
+            ans = cps_by_em_size.ans = 16
+        else:
+            d = document.createElement('span')
+            d.style.position = 'absolute'
+            d.style.visibility = 'hidden'
+            d.style.width = '1rem'
+            d.style.fontSize = '1rem'
+            d.style.paddingTop = d.style.paddingBottom = d.style.paddingLeft = d.style.paddingRight = '0'
+            d.style.marginTop = d.style.marginBottom = d.style.marginLeft = d.style.marginRight = '0'
+            d.style.borderStyle = 'none'
+            document.body.appendChild(d)
+            w = d.clientWidth
+            document.body.removeChild(d)
+            ans = cps_by_em_size.ans = max(2, w)
         cps_by_em_size.at_font_size = fs
     return ans