diff --git a/dedal/spack_factory/SpackOperation.py b/dedal/spack_factory/SpackOperation.py
index 7814cc8b6b698ecda6c3dbacddc36c331bd1526f..ad4f2389edc1c278cfe91eb166be0dc51f60757a 100644
--- a/dedal/spack_factory/SpackOperation.py
+++ b/dedal/spack_factory/SpackOperation.py
@@ -220,7 +220,7 @@ class SpackOperation:
         result = self.command_runner.run_preconfigured_command_sequence(
             PreconfiguredCommandEnum.SPACK_MIRROR_ADD,
             self.spack_setup_script,
-            "" if global_mirror else self.env_path,
+            "" if global_mirror else str(self.env_path),
             mirror_name,
             mirror_path,
             autopush,