diff --git a/collects/compiler/sig.ss b/collects/compiler/sig.ss
index 7839a8694d..e268f43852 100644
--- a/collects/compiler/sig.ss
+++ b/collects/compiler/sig.ss
@@ -21,6 +21,10 @@
    use-mrspidey-for-units ; #t => per-unit analyze with MrSpidey
                           ; default = #f
 
+   lightweight ; #t => perform lightweight closure conversion
+               ;       on MrSpidey-analyzed code
+               ;       default = #t
+
    clean-intermediate-files ; #t => keep intermediate .c/.o files
                             ; default = #f