diff --git a/nixos/modules/services/mail/dovecot.nix b/nixos/modules/services/mail/dovecot.nix
index 25c7017a1d25..79c8fec75252 100644
--- a/nixos/modules/services/mail/dovecot.nix
+++ b/nixos/modules/services/mail/dovecot.nix
@@ -119,9 +119,10 @@ let
     ''
       plugin {
         sieve_plugins = ${concatStringsSep " " cfg.sieve.plugins}
-        sieve_extensions = ${concatStringsSep " " (map (el: "+${el}") cfg.sieve.extensions)}
-        sieve_global_extensions = ${concatStringsSep " " (map (el: "+${el}") cfg.sieve.globalExtensions)}
     ''
+    (optionalString (cfg.sieve.extensions != []) ''sieve_extensions = ${concatMapStringsSep " " (el: "+${el}") cfg.sieve.extensions}'')
+    (optionalString (cfg.sieve.globalExtensions != []) ''sieve_global_extensions = ${concatMapStringsSep " " (el: "+${el}") cfg.sieve.globalExtensions}'')
+
     (optionalString (cfg.imapsieve.mailbox != []) ''
       ${
         concatStringsSep "\n" (flatten (imap1 (