diff --git a/json/src/com/jetbrains/jsonSchema/impl/JsonSchemaObject.java b/json/src/com/jetbrains/jsonSchema/impl/JsonSchemaObject.java
index 98b302a3389e..ca2b3fd21e1b 100644
--- a/json/src/com/jetbrains/jsonSchema/impl/JsonSchemaObject.java
+++ b/json/src/com/jetbrains/jsonSchema/impl/JsonSchemaObject.java
@@ -280,7 +280,7 @@ public class JsonSchemaObject {
     if (other.myNot != null) myNot = other.myNot;
     if (other.myIfThenElse != null) {
       if (myIfThenElse == null) myIfThenElse = other.myIfThenElse;
-      else myIfThenElse.addAll(other.myIfThenElse);
+      else myIfThenElse = ContainerUtil.concat(myIfThenElse, other.myIfThenElse);
     }
     myShouldValidateAgainstJSType |= other.myShouldValidateAgainstJSType;
   }