diff --git a/Configuration.md b/Configuration.md
index b6a3ac1..f484f3a 100644
--- a/Configuration.md
+++ b/Configuration.md
@@ -33,4 +33,5 @@ If you wanna use want to revert changes or view older revisions of entities, the
 ### Other / less used options
 * `DEMO_MODE`: Set Part-DB into demo mode, which forbids users to change their passwords and settings. Used for the demo instance, should not be needed for normal installations.
 * `NO_URL_REWRITE_AVAILABLE` (allowed values `true` or `false`): Set this value to true, if your webserver does not support rewrite. In this case, all URL pathes will contain index.php/, which is needed then. Normally this setting do not need to be changed.
-* `FIXER_API_KEY`: If you want to automatically retrieve exchange rates for base currencies other than euros, you have configure an exchange rate provider API. [Fixer.io](https://fixer.io/) is preconfigured, and you just have to register there and set the retrieved API key in this environment variable.
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+* `FIXER_API_KEY`: If you want to automatically retrieve exchange rates for base currencies other than euros, you have configure an exchange rate provider API. [Fixer.io](https://fixer.io/) is preconfigured, and you just have to register there and set the retrieved API key in this environment variable.
+* `APP_ENV`: This value should always be set to `prod` in normal use. Set it to `dev` to enable debug/development mode. (**You should not do this on a publicly accessible server, as it will leak sensitive informations!**)
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