diff --git a/backend/Kildall.v b/backend/Kildall.v
index 4379b00fca9fa127c46c929c32dc574cf1842c52..41011f2b14411784768f9d5dee62e0a3cd039baa 100644
--- a/backend/Kildall.v
+++ b/backend/Kildall.v
@@ -147,7 +147,7 @@ Record state : Set :=
             compute in = lub st_in[s] out
             if in <> st_in[s]:
                 st_in[s] := in
-                st_wrk := st_wrk union {n}
+                st_wrk := st_wrk union {s}
             end if
         end for
     end while