diff --git a/nixos/modules/services/mail/opendkim.nix b/nixos/modules/services/mail/opendkim.nix
index 9bf6f338d93e..beff57613afc 100644
--- a/nixos/modules/services/mail/opendkim.nix
+++ b/nixos/modules/services/mail/opendkim.nix
@@ -134,7 +134,7 @@ in {
         ReadWritePaths = [ cfg.keyPath ];
 
         AmbientCapabilities = [];
-        CapabilityBoundingSet = [];
+        CapabilityBoundingSet = "";
         DevicePolicy = "closed";
         LockPersonality = true;
         MemoryDenyWriteExecute = true;
diff --git a/nixos/modules/services/mail/rspamd.nix b/nixos/modules/services/mail/rspamd.nix
index 2f9d28195bd8..473ddd52357d 100644
--- a/nixos/modules/services/mail/rspamd.nix
+++ b/nixos/modules/services/mail/rspamd.nix
@@ -410,7 +410,7 @@ in
         StateDirectoryMode = "0700";
 
         AmbientCapabilities = [];
-        CapabilityBoundingSet = [];
+        CapabilityBoundingSet = "";
         DevicePolicy = "closed";
         LockPersonality = true;
         NoNewPrivileges = true;