Index: src/builtins/control.pir
===================================================================
--- src/builtins/control.pir	(revision 29737)
+++ src/builtins/control.pir	(working copy)
@@ -115,6 +115,7 @@
 .sub 'sleep'
     .param num a
     sleep a
+    .return (a)
 .end
 
 =item eval