diff --git a/install-mpsd-software-environment.py b/install-mpsd-software-environment.py
index e09c1a7362314432a96abf1a48ffcf3083c531d8..05401ebd3ce8b077cb8f4d29ffe41c565c352359 100755
--- a/install-mpsd-software-environment.py
+++ b/install-mpsd-software-environment.py
@@ -157,7 +157,7 @@ def main():
         if args.target_dir:
             target_dir = args.target_dir
         else:
-            mpsd_os os.getenv('MPSD_OS','UNKNOWN_OS')
+            mpsd_os = os.getenv('MPSD_OS','UNKNOWN_OS')
             mpsd_arch = os.getenv('MPSD_ARCH','UNKNOWN_ARCH')
             if os.path.exists('/opt_mpsd'):
                 root_dir = '/opt_mpsd'