diff --git a/pkgs/tools/admin/simp_le/default.nix b/pkgs/tools/admin/simp_le/default.nix
index 5bfc00ac000..393d9d145c2 100644
--- a/pkgs/tools/admin/simp_le/default.nix
+++ b/pkgs/tools/admin/simp_le/default.nix
@@ -22,6 +22,8 @@ python3Packages.buildPythonApplication rec {
 
   propagatedBuildInputs = with python3Packages; [ acme setuptools_scm josepy idna ];
 
+  checkInputs = with python3Packages; [ mock ];
+
   meta = with lib; {
     homepage = "https://github.com/zenhack/simp_le";
     description = "Simple Let's Encrypt client";