diff --git a/nixos/modules/services/networking/flashpolicyd.nix b/nixos/modules/services/networking/flashpolicyd.nix
index 7f25083307c7..d3ac78430ca3 100644
--- a/nixos/modules/services/networking/flashpolicyd.nix
+++ b/nixos/modules/services/networking/flashpolicyd.nix
@@ -50,6 +50,7 @@ in
       };
 
       policy = mkOption {
+        type = types.lines;
         default =
           ''
             <?xml version="1.0"?>