diff --git a/Kernel/setSubstitutionSystem$cpp.m b/Kernel/setSubstitutionSystem$cpp.m
index ea73b25c9..0a09b6ea5 100644
--- a/Kernel/setSubstitutionSystem$cpp.m
+++ b/Kernel/setSubstitutionSystem$cpp.m
@@ -77,8 +77,8 @@
    sublists. *)
 (* This format is used to pass both rules and set data into libSetReplace over LibraryLink *)
 
-encodeNestedLists[list_List] :=
-    {list} //. {{l___, List[args___], r___} :> {l, Length[{args}], args, r}}
+encodeNestedLists[list_List] := Flatten @ {Length @ list, encodeNestedLists /@ list}
+encodeNestedLists[arg_] := arg
 
 (* This is the reverse, used to decode set data (a list of expressions) from libSetReplace *)