diff --git a/gtk/setupwizard.c b/gtk/setupwizard.c
index 0c15e602b..439f9c89f 100644
--- a/gtk/setupwizard.c
+++ b/gtk/setupwizard.c
@@ -422,11 +422,17 @@ static void linphone_gtk_assistant_prepare(GtkWidget *assistant, GtkWidget *page
 
 		gchar *username = creator->username + 4;
 		const gchar *needle = "@";
-		username = g_strndup(username, (g_strrstr(username, needle) - username));
+		const gchar *needle_ptr = g_strrstr(username, needle);
+		if (needle_ptr != NULL) {
+			username = g_strndup(username, needle_ptr - username);
+		} else {
+			username = g_strdup(username);
+		}
 		gchar domain[128];
 		g_snprintf(domain, sizeof(domain), "\"%s\"", creator->domain + 4);
 		LinphoneAuthInfo *info=linphone_auth_info_new(username, username, creator->password, NULL, domain);
 		linphone_core_add_auth_info(linphone_gtk_get_core(),info);
+		g_free(username);
 
 		if (linphone_core_add_proxy_config(linphone_gtk_get_core(),cfg)==-1)
 			return;