diff --git a/jscomp/core/js_exp_make.ml b/jscomp/core/js_exp_make.ml
index bf9fd5b272..bc137a85c2 100644
--- a/jscomp/core/js_exp_make.ml
+++ b/jscomp/core/js_exp_make.ml
@@ -176,6 +176,10 @@ let typeof ?comment (e : t) : t =
 let instanceof ?comment (e0 : t) (e1: t) : t =
   { expression_desc = Bin (InstanceOf, e0, e1); comment }
 
+let is_array  (e0 : t) : t =
+  let f = str "Array.isArray" ~delim:DNoQuotes in
+  { expression_desc = Call (f, [e0], Js_call_info.ml_full_call); comment=None }
+  
 let new_ ?comment e0 args : t =
   { expression_desc = New (e0, Some args); comment }
 
diff --git a/jscomp/core/js_exp_make.mli b/jscomp/core/js_exp_make.mli
index d2590e422b..5fcf6b4039 100644
--- a/jscomp/core/js_exp_make.mli
+++ b/jscomp/core/js_exp_make.mli
@@ -212,6 +212,7 @@ val is_type_object : t -> t
 
 val typeof : ?comment:string -> t -> t
 val instanceof : ?comment:string -> t -> t -> t
+val is_array : t -> t
 
 val to_int32 : ?comment:string -> t -> t
 
diff --git a/jscomp/core/lam_compile.ml b/jscomp/core/lam_compile.ml
index 24943156c0..d4c320ce59 100644
--- a/jscomp/core/lam_compile.ml
+++ b/jscomp/core/lam_compile.ml
@@ -749,7 +749,7 @@ and compile_untagged_cases cxt switch_exp table default =
   | Block StringType
   | Block FloatType
   | Block Object -> E.string_equal (E.typeof y) x 
-  | Block Array -> E.instanceof y x
+  | Block Array -> E.is_array y
   | Block Unknown ->
     (* This should not happen because unknown must be the only non-literal case *)
     assert false 
@@ -767,7 +767,7 @@ and compile_untagged_cases cxt switch_exp table default =
     match array_clauses with
     | [(l, {J.switch_body})] when List.length clauses > 1 ->
       let rest = Ext_list.filter clauses (fun c -> not (is_array c)) in
-      S.if_ (E.instanceof e (E.literal l))
+      S.if_ (E.is_array e)
         (switch_body)
         ~else_:([S.string_switch ?default ?declaration (E.typeof e) rest])
     | _ :: _ :: _ -> assert false (* at most 1 array case *)
diff --git a/jscomp/test/UntaggedVariants.js b/jscomp/test/UntaggedVariants.js
index 79b0d8c375..27283b73b8 100644
--- a/jscomp/test/UntaggedVariants.js
+++ b/jscomp/test/UntaggedVariants.js
@@ -154,7 +154,7 @@ var OnlyBlocks = {
 };
 
 function classify$5(x) {
-  if (x instanceof Array) {
+  if (Array.isArray(x)) {
     return "array";
   }
   switch (typeof x) {
@@ -184,7 +184,7 @@ function classify$6(x) {
       
     }
   } else {
-    if (x instanceof Array) {
+    if (Array.isArray(x)) {
       return {
               TAG: "JSONArray",
               _0: x