diff --git a/nixos/modules/services/networking/cntlm.nix b/nixos/modules/services/networking/cntlm.nix
index c8e08fdefaa4..eea28e12ce0e 100644
--- a/nixos/modules/services/networking/cntlm.nix
+++ b/nixos/modules/services/networking/cntlm.nix
@@ -36,12 +36,14 @@ in
     enable = mkEnableOption "cntlm, which starts a local proxy";
 
     username = mkOption {
+      type = types.str;
       description = ''
         Proxy account name, without the possibility to include domain name ('at' sign is interpreted literally).
       '';
     };
 
     domain = mkOption {
+      type = types.str;
       description = "Proxy account domain/workgroup name.";
     };
 
@@ -60,6 +62,7 @@ in
     };
 
     proxy = mkOption {
+      type = types.listOf types.str;
       description = ''
         A list of NTLM/NTLMv2 authenticating HTTP proxies.
 
@@ -75,11 +78,13 @@ in
         A list of domains where the proxy is skipped.
       '';
       default = [];
+      type = types.listOf types.str;
       example = [ "*.example.com" "example.com" ];
     };
 
     port = mkOption {
       default = [3128];
+      type = types.listOf types.port;
       description = "Specifies on which ports the cntlm daemon listens.";
     };