diff --git a/site/content/docs/4.3/getting-started/theming.md b/site/content/docs/4.3/getting-started/theming.md
index 9c34c9ee3f..1703770e70 100644
--- a/site/content/docs/4.3/getting-started/theming.md
+++ b/site/content/docs/4.3/getting-started/theming.md
@@ -373,6 +373,10 @@ Here are the variables we include (note that the `:root` is required). They're l
 {{- $css := readFile "dist/css/bootstrap.css" -}}
 {{- $match := findRE ":root {([^}]*)}" $css 1 -}}
 
+{{- if (eq (len $match) 0) -}}
+{{- errorf "Got no matches for :root in %q!" $.Page.Path -}}
+{{- end -}}
+
 {{- index $match 0 -}}
 
 {{< /root.inline >}}