diff --git a/modules/programs/git.nix b/modules/programs/git.nix
index dfdac2d4b..f78cfc0b8 100644
--- a/modules/programs/git.nix
+++ b/modules/programs/git.nix
@@ -18,6 +18,7 @@ let
     options = {
       key = mkOption {
         type = types.nullOr types.str;
+        default = null;
         description = ''
           The default GPG signing key fingerprint.