diff --git a/htdocs/core/class/conf.class.php b/htdocs/core/class/conf.class.php
index 9a804256dac..38538f12f93 100644
--- a/htdocs/core/class/conf.class.php
+++ b/htdocs/core/class/conf.class.php
@@ -171,6 +171,13 @@ class Conf
 				$value = $objp->value;
 				if ($key)
 				{
+					// Allow constants values to be overridden by environment variables
+					if (isset($_SERVER['DOLIBARR_' . $key])) {
+						$value=$_SERVER['DOLIBARR_' . $key];
+					} elseif (isset($_ENV['DOLIBARR_' . $key])) {
+						$value=$_ENV['DOLIBARR_' . $key];
+					}
+
 					//if (! defined("$key")) define("$key", $value);	// In some cases, the constant might be already forced (Example: SYSLOG_HANDLERS during install)
 					$this->global->$key = $value;