diff --git a/management/ssl_certificates.py b/management/ssl_certificates.py
index f7d481a8..ce72cc6d 100755
--- a/management/ssl_certificates.py
+++ b/management/ssl_certificates.py
@@ -671,8 +671,7 @@ def get_certificate_domains(cert):
 
 	try:
 		sans = cert.extensions.get_extension_for_oid(OID_SUBJECT_ALTERNATIVE_NAME).value.get_values_for_type(DNSName)
-		for san in sans:
-			names.add(idna_decode_dns_name(san))
+		names.update(idna_decode_dns_name(san) for san in sans)
 	except ExtensionNotFound:
 		pass