diff --git a/nixos/modules/services/mail/opendkim.nix b/nixos/modules/services/mail/opendkim.nix
index 9bf6f338d93..beff57613af 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;