diff --git a/compiler/jslang/jsCons.ml b/compiler/jslang/jsCons.ml
index 4ecf2645..da9d377b 100644
--- a/compiler/jslang/jsCons.ml
+++ b/compiler/jslang/jsCons.ml
@@ -75,7 +75,7 @@ struct
   let true_ ?label () = bool ?label true
   let false_ ?label () = bool ?label false
 
-  let call ?(label=def_label()) ~pure f args =
+  let call ?(label=def_label()) ?(pure=false) f args =
     J.Je_call (label, f, args, pure)
 
   let comma ?(label=def_label()) list last =
diff --git a/compiler/jslang/jsCons.mli b/compiler/jslang/jsCons.mli
index fb75f108..b715ff38 100644
--- a/compiler/jslang/jsCons.mli
+++ b/compiler/jslang/jsCons.mli
@@ -32,7 +32,7 @@ sig
   val false_ : ?label:Annot.label -> unit -> JsAst.expr
 
   val bool : ?label:Annot.label -> bool -> JsAst.expr
-  val call : ?label:Annot.label -> pure:bool -> JsAst.expr -> JsAst.expr list -> JsAst.expr
+  val call : ?label:Annot.label -> ?pure:bool -> JsAst.expr -> JsAst.expr list -> JsAst.expr
   val cond : ?label:Annot.label -> JsAst.expr -> JsAst.expr -> JsAst.expr -> JsAst.expr
 
   (**