diff --git a/docs/sources/panels/configure-standard-options/index.md b/docs/sources/panels/configure-standard-options/index.md
index 587d297362b..ca7da3050dc 100644
--- a/docs/sources/panels/configure-standard-options/index.md
+++ b/docs/sources/panels/configure-standard-options/index.md
@@ -54,6 +54,7 @@ You can use the unit dropdown to also specify custom units, custom prefix or suf
 To select a custom unit enter the unit and select the last `Custom: xxx` option in the dropdown.
 
 - `suffix:<suffix>` for custom unit that should go after value.
+- `prefix:<prefix>` for custom unit that should go before value.
 - `time:<format>` For custom date time formats type for example `time:YYYY-MM-DD`. See [formats](https://momentjs.com/docs/#/displaying/) for the format syntax and options.
 - `si:<base scale><unit characters>` for custom SI units. For example: `si: mF`. This one is a bit more advanced as you can specify both a unit and the
   source data scale. So if your source data is represented as milli (thousands of) something prefix the unit with that