diff --git a/inst/resources/gitbook/js/plugin-fontsettings.js b/inst/resources/gitbook/js/plugin-fontsettings.js
index e8513560f..df2651b14 100644
--- a/inst/resources/gitbook/js/plugin-fontsettings.js
+++ b/inst/resources/gitbook/js/plugin-fontsettings.js
@@ -88,7 +88,8 @@ gitbook.require(["gitbook", "lodash", "jQuery"], function(gitbook, _, $) {
             $book[0].className = $book[0].className.replace(/\bcolor-theme-\S+/g, '');
             $book.addClass("color-theme-"+fontState.theme);
         }
-        $book.find('section').css('line-height', fontState.spacing / 10);
+        var lineHeight = Math.max(fontState.spacing / 10, 1);
+        $book.find('section').css('line-height', lineHeight);
     };
 
     function init(config) {