diff --git a/pkgs/development/python-modules/w1thermsensor/default.nix b/pkgs/development/python-modules/w1thermsensor/default.nix
index a60c545a2536..58158f77282b 100644
--- a/pkgs/development/python-modules/w1thermsensor/default.nix
+++ b/pkgs/development/python-modules/w1thermsensor/default.nix
@@ -35,10 +35,15 @@ buildPythonPackage rec {
   ];
 
   propagatedBuildInputs = [
-    aiofiles
     click
   ];
 
+  passthru.optional-dependencies = {
+    async = [
+      aiofiles
+    ];
+  };
+
   # Don't try to load the kernel module in tests.
   env.W1THERMSENSOR_NO_KERNEL_MODULE = 1;