diff --git a/book/book.toml b/book/book.toml
index f2621c433..c7cf5c0b1 100644
--- a/book/book.toml
+++ b/book/book.toml
@@ -50,8 +50,8 @@ sansfontoptions = [
 ]
 # You can get these fonts here: https://fonts.google.com/selection?query=noto+color+
 monofont = "Noto Sans Mono"
-mainfontfallback = ["Open Sans"]
-sansfontfallback = ["Open Sans"]
+mainfontfallback = ["Open Sans:style=Regular"]
+sansfontfallback = ["Open Sans:style=Regular"]
 monofontfallback = [
   "Noto Color Emoji:mode=harf",
 ]
@@ -91,8 +91,8 @@ sansfontoptions = [
 ]
 # You can get these fonts here: https://fonts.google.com/selection?query=noto+color+
 monofont = "Noto Sans Mono"
-mainfontfallback = ["Open Sans"]
-sansfontfallback = ["Open Sans"]
+mainfontfallback = ["Open Sans:style=Regular"]
+sansfontfallback = ["Open Sans:style=Regular"]
 monofontfallback = [
   "Noto Color Emoji:mode=harf",
 ]
@@ -122,8 +122,8 @@ metadata-file = "metadata.yml"
 [output.pandoc.profile.html.variables]
 # You can get these fonts here: https://fonts.google.com/selection?query=noto+color+
 monofont = "Noto Sans Mono"
-mainfontfallback = ["Open Sans"]
-sansfontfallback = ["Open Sans"]
+mainfontfallback = ["Open Sans:style=Regular"]
+sansfontfallback = ["Open Sans:style=Regular"]
 monofontfallback = [
   "Noto Color Emoji:mode=harf",
 ]