diff --git a/modoboa/admin/management/commands/subcommands/_mx.py b/modoboa/admin/management/commands/subcommands/_mx.py
index e7460e360..22dce6177 100644
--- a/modoboa/admin/management/commands/subcommands/_mx.py
+++ b/modoboa/admin/management/commands/subcommands/_mx.py
@@ -82,8 +82,9 @@ class CheckMXRecords(BaseCommand):
         """Store DNSBL provider results for domain."""
         alerts = {}
         to_create = []
-        for mx in results.keys():
-            result = "" if not results[mx] else results[mx]
+        for mx, result in list(results.items()):
+            if not result:
+                result = ""
             dnsbl_result = models.DNSBLResult.objects.filter(
                 domain=domain, provider=provider, mx=mx).first()
             trigger = False