diff --git a/js/js.libraries/src/core/json.kt b/js/js.libraries/src/core/json.kt
index 355ff921d11..fb2af70372d 100644
--- a/js/js.libraries/src/core/json.kt
+++ b/js/js.libraries/src/core/json.kt
@@ -74,9 +74,9 @@ public fun Json.add(other: Json): Json {
  */
 public external object JSON {
     public fun stringify(o: Any?): String
-    public fun stringify(o: Any?, replacer: (key: String, value: Any?) -> Any?): String
-    public fun stringify(o: Any?, replacer: (key: String, value: Any?) -> Any?, space: Int): String
-    public fun stringify(o: Any?, replacer: (key: String, value: Any?) -> Any?, space: String): String
+    public fun stringify(o: Any?, replacer: ((key: String, value: Any?) -> Any?)): String
+    public fun stringify(o: Any?, replacer: ((key: String, value: Any?) -> Any?)? = definedExternally, space: Int): String
+    public fun stringify(o: Any?, replacer: ((key: String, value: Any?) -> Any?)? = definedExternally, space: String): String
     public fun stringify(o: Any?, replacer: Array<String>): String
     public fun stringify(o: Any?, replacer: Array<String>, space: Int): String
     public fun stringify(o: Any?, replacer: Array<String>, space: String): String