diff --git a/layouts/partials/scripts/mermaid.html b/layouts/partials/scripts/mermaid.html
index 20cdab3e48..6ea757a8df 100644
--- a/layouts/partials/scripts/mermaid.html
+++ b/layouts/partials/scripts/mermaid.html
@@ -18,7 +18,7 @@
         return;
     }
 
-    var params = {{ .Site.Params.mermaid | jsonify | safeJS }};
+    var params = {{ with .Site.Params.mermaid }}{{ . | jsonify | safeJS }}{{ else }}{}{{- end }};
 
     // Site params are stored with lowercase keys; lookup correct casing
     // from Mermaid default config.
diff --git a/userguide/content/en/docs/adding-content/diagrams-and-formulae/index.md b/userguide/content/en/docs/adding-content/diagrams-and-formulae/index.md
index 4349127abf..21163d946f 100644
--- a/userguide/content/en/docs/adding-content/diagrams-and-formulae/index.md
+++ b/userguide/content/en/docs/adding-content/diagrams-and-formulae/index.md
@@ -388,18 +388,18 @@ By default, docsy pulls in the latest officially released version of Mermaid at
 {{< tab header="Configuration file:" disabled=true />}}
 {{< tab header="hugo.toml" lang="toml" >}}
 [params.mermaid]
-version = "10.8.0"
+version = "10.9.0"
 {{< /tab >}}
 {{< tab header="hugo.yaml" lang="yaml" >}}
 params:
   mermaid:
-    version: 10.8.0
+    version: 10.9.0
 {{< /tab >}}
 {{< tab header="hugo.json" lang="json" >}}
 {
   "params": {
     "mermaid": {
-      "version": "10.8.0"
+      "version": "10.9.0"
     }
   }
 }