diff --git a/lib/runners.py b/lib/runners.py
index 687e851..7fc044b 100644
--- a/lib/runners.py
+++ b/lib/runners.py
@@ -20,6 +20,7 @@ def _build_script(cmd_def):
         os.write(fh, '\n')
     os.write(fh, cmd_def['cmd'])
     os.write(fh, '\n')
+    os.close(fh)
 
     # ensure that the filepath is executable by the runner process, the default
     # tempfile is 0600