diff --git a/pkgs/tools/security/onlykey-agent/default.nix b/pkgs/tools/security/onlykey-agent/default.nix
index bdbf881396e9..f37073d602da 100644
--- a/pkgs/tools/security/onlykey-agent/default.nix
+++ b/pkgs/tools/security/onlykey-agent/default.nix
@@ -26,6 +26,7 @@ let
     propagatedBuildInputs = oa.propagatedBuildInputs or [ ] ++ [
       bech32
       cryptography
+      cython
       docutils
       pycryptodome
       pynacl
@@ -52,7 +53,7 @@ python3Packages.buildPythonApplication rec {
     sha256 = "sha256-SbGb7CjcD7cFPvASZtip56B4uxRiFKZBvbsf6sb8fds=";
   };
 
-  propagatedBuildInputs = with python3Packages; [ lib-agent onlykey-cli setuptools cython ];
+  propagatedBuildInputs = with python3Packages; [ lib-agent onlykey-cli setuptools ];
 
   # move the python library into the sitePackages.
   postInstall = ''