Index: litsupport/run_under.py
===================================================================
--- litsupport/run_under.py
+++ litsupport/run_under.py
@@ -3,7 +3,19 @@
 
 
 def mutateCommandLine(context, commandline):
-    return context.config.run_under + " " + commandline
+    cmd = shellcommand.parse(commandline)
+    run_under_cmd = shellcommand.parse(context.config.run_under)
+
+    if (run_under_cmd.stdin is not None or
+        run_under_cmd.stdout is not None or
+        run_under_cmd.stderr is not None or
+        run_under_cmd.workdir is not None or
+        run_under_cmd.envvars):
+        raise Exception("invalid run_under argument!")
+
+    cmd.wrap(run_under_cmd.executable, run_under_cmd.arguments)
+
+    return cmd.toCommandline()
 
 
 def mutatePlan(context, plan):