diff --git a/nginx_configurator/certs.py b/nginx_configurator/certs.py
index 4c98384..d6fcf8e 100644
--- a/nginx_configurator/certs.py
+++ b/nginx_configurator/certs.py
@@ -51,7 +51,7 @@ def gather_autossl_directives(nginx_conf: Path):
                     f"Cannot get SSL cert for \"{''.join(domains)}\". Invalid domains."
                 )
 
-            if not re.match(r"^[a-zA-Z0-9-_]$", alias):
+            if not re.match(r"^[a-zA-Z0-9-_]+$", alias):
                 raise ValueError(f'Invalid cert alias "{alias}"')
 
             directives.append((domains, alias))