diff --git a/content/functions/isset.md b/content/functions/isset.md
index 1e737dfe5..3757f54ef 100644
--- a/content/functions/isset.md
+++ b/content/functions/isset.md
@@ -17,10 +17,13 @@ deprecated: false
 aliases: []
 ---
 
-`isset` returns true if the parameter is set.
-Takes either a slice, array or channel and an index or a map and a key as input.
+`isset` returns true if the parameter is set. Takes either a slice, array, or channel and an index or a map and a key as input.
 
 ```
 {{ if isset .Params "project_url" }} {{ index .Params "project_url" }}{{ end }}
 ```
 
+{{% warning %}}
+All site-level configuration keys are stored as lower case. Therefore, a `myParam` key-value set in your [site configuration file](/getting-started/configuration/) needs to be accessed with `{{if isset .Site.Params "myparam"}}` and *not* with `{{if isset .Site.Params "myParam"}}`. Note that you can still access the same config key with `.Site.Params.myParam` *or* `.Site.Params.myparam`, for example, when using [`with`](/functions/with).
+{{% /warning %}}
+