diff --git a/apps/readest-app/src/utils/style.ts b/apps/readest-app/src/utils/style.ts
index 9c0d6686..42280ca0 100644
--- a/apps/readest-app/src/utils/style.ts
+++ b/apps/readest-app/src/utils/style.ts
@@ -794,9 +794,9 @@ export const transformStylesheet = (css: string, vw: number, vh: number, vertica
     .replace(/([\s;])-o-user-select\s*:\s*none/gi, '$1-o-user-select: unset')
     .replace(/([\s;])user-select\s*:\s*none/gi, '$1user-select: unset')
     .replace(/(font-family\s*:[^;]*?)\bsans-serif\b/gi, '$1READEST_SS_PLACEHOLDER')
-    .replace(/(font-family\s*:[^;]*?)\bserif\b(?!-)/gi, '$1var(--serif)')
-    .replace(/READEST_SS_PLACEHOLDER/g, 'var(--sans-serif)')
-    .replace(/(font-family\s*:[^;]*?)\bmonospace\b/gi, '$1var(--monospace)')
+    .replace(/(font-family\s*:[^;]*?)\bserif\b(?!-)/gi, '$1var(--serif, serif)')
+    .replace(/READEST_SS_PLACEHOLDER/g, 'var(--sans-serif, sans-serif)')
+    .replace(/(font-family\s*:[^;]*?)\bmonospace\b/gi, '$1var(--monospace, monospace)')
     .replace(/([\s;])font-weight\s*:\s*normal/gi, '$1font-weight: var(--font-weight)')
     .replace(/([\s;])color\s*:\s*black/gi, '$1color: var(--theme-fg-color)')
     .replace(/([\s;])color\s*:\s*#000000/gi, '$1color: var(--theme-fg-color)')
diff --git a/packages/foliate-js b/packages/foliate-js
index 2300db0d..837c98fa 160000
--- a/packages/foliate-js
+++ b/packages/foliate-js
@@ -1 +1 @@
-Subproject commit 2300db0dee97dd4879e1c50e16464a56c9161669
+Subproject commit 837c98fae0c39d1cc1cc892408910c2135f8ad0b