diff --git a/ecrire/inc/mutualiser.php b/ecrire/inc/mutualiser.php
index 1be236d1755320b940f00776192076f9f5b22fa8..9dc7667f0b9d3995bcb5a5bba96d5b71cba09f26 100644
--- a/ecrire/inc/mutualiser.php
+++ b/ecrire/inc/mutualiser.php
@@ -32,9 +32,12 @@ function demarrer_site($site = '', $options = array()) {
 	);
 
 	// Le prefixe = max 10 caracteres a-z0-9, qui ressemblent au domaine
+	// et ne commencent pas par un chiffre
 	if ($options['cookie_prefix'] OR $options['table_prefix']) {
 		$prefix = preg_replace(',^www\.|[^a-z0-9],', '', strtolower($site));
 		$prefix = substr($prefix, 0, 10);
+		if (!preg_match(',^[a-z],', $prefix))
+			$prefix = 'a'.$prefix;
 		if ($options['cookie_prefix'])
 			$GLOBALS['cookie_prefix'] = $prefix;
 		if ($options['table_prefix'])