diff --git a/modules/home-manager/cli/git/default.nix b/modules/home-manager/cli/git/default.nix
index e46fba6..520adcb 100644
--- a/modules/home-manager/cli/git/default.nix
+++ b/modules/home-manager/cli/git/default.nix
@@ -20,7 +20,7 @@ in
     };
 
     signingKey = mkOption {
-      type = types.str;
+      type = types.nullOr types.str;
       default = null;
       description = "signing key fingerprint";
     };
@@ -46,7 +46,7 @@ in
       package = pkgs.gitFull;
       userName = "${cfg.userName}";
       userEmail = "${cfg.userEmail}";
-      signing.key = "${cfg.signingKey}";
+      signing.key = cfg.signingKey;
       signing.signByDefault = cfg.signByDefault;
       aliases = {
         co = "checkout";