diff --git a/nixos/modules/virtualisation/docker.nix b/nixos/modules/virtualisation/docker.nix
index 5be76b2682f5..49170f2220bc 100644
--- a/nixos/modules/virtualisation/docker.nix
+++ b/nixos/modules/virtualisation/docker.nix
@@ -45,7 +45,7 @@ in
       };
     extraOptions =
       mkOption {
-        type = types.str;
+        type = types.separatedString " ";
         default = "";
         description =
           ''