diff --git a/docs/ubuntu-installation.md b/docs/ubuntu-installation.md
index 79a088805..4f379a53f 100644
--- a/docs/ubuntu-installation.md
+++ b/docs/ubuntu-installation.md
@@ -32,7 +32,7 @@ You can overwrite the files of the folder `system` by setting an environment var
 For example to write the content of the repository [github.com/xpetit/custom](github.com/xpetit/custom) in the system folder :
 
 ```shell
-export 'OVERWRITE=.;https://github.com/xpetit/custom.git'
+export OVERWRITE='.;https://github.com/xpetit/custom.git'
 ```
 
 ## OS configuration