diff --git a/Makefile b/Makefile
index 75e9330..b6c98ff 100644
--- a/Makefile
+++ b/Makefile
@@ -7,5 +7,4 @@ apidoc:
 	smldoc --windowtitle="SU4SML API Documentation" --hidebysig --directory=doc/api --linksource --showsummary --overview=doc/overview.html src/su4sml.cm
 
 su4sml:
-	cd src && echo "val _ = use \"ROOT.ML\"" | sml
-	
+	cd src && echo "val _ = use \"ROOT.ML\"; val _ = OS.Process.exit OS.Process.success" | sml