diff --git a/nixos/modules/programs/ssh.nix b/nixos/modules/programs/ssh.nix
index c9bfe2fe0f7..796740ea636 100644
--- a/nixos/modules/programs/ssh.nix
+++ b/nixos/modules/programs/ssh.nix
@@ -61,7 +61,8 @@ in
 
       agentTimeout = mkOption {
         type = types.nullOr types.string;
-        default = "1h";
+        default = null;
+        example = "1h";
         description = ''
           How long to keep the private keys in memory. Use null to keep them forever.
         '';