diff --git a/js/js.frontend/src/org/jetbrains/kotlin/js/descriptorUtils/descriptorUtils.kt b/js/js.frontend/src/org/jetbrains/kotlin/js/descriptorUtils/descriptorUtils.kt
index 207938a7ccf..0805753abc7 100644
--- a/js/js.frontend/src/org/jetbrains/kotlin/js/descriptorUtils/descriptorUtils.kt
+++ b/js/js.frontend/src/org/jetbrains/kotlin/js/descriptorUtils/descriptorUtils.kt
@@ -1,17 +1,6 @@
 /*
- * Copyright 2010-2016 JetBrains s.r.o.
- *
- * Licensed under the Apache License, Version 2.0 (the "License");
- * you may not use this file except in compliance with the License.
- * You may obtain a copy of the License at
- *
- * http://www.apache.org/licenses/LICENSE-2.0
- *
- * Unless required by applicable law or agreed to in writing, software
- * distributed under the License is distributed on an "AS IS" BASIS,
- * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
- * See the License for the specific language governing permissions and
- * limitations under the License.
+ * Copyright 2010-2020 JetBrains s.r.o. and Kotlin Programming Language contributors.
+ * Use of this source code is governed by the Apache 2.0 license that can be found in the license/LICENSE.txt file.
  */
 
 package org.jetbrains.kotlin.js.descriptorUtils
@@ -31,7 +20,9 @@ val KotlinType.nameIfStandardType: Name?
     get() = constructor.declarationDescriptor?.takeIf(KotlinBuiltIns::isBuiltIn)?.name
 
 fun KotlinType.getJetTypeFqName(printTypeArguments: Boolean): String {
-    val declaration = requireNotNull(constructor.declarationDescriptor)
+    val declaration = requireNotNull(constructor.declarationDescriptor) {
+        "declarationDescriptor is null for constructor = $constructor with ${constructor.javaClass}"
+    }
     if (declaration is TypeParameterDescriptor) {
         return StringUtil.join(declaration.upperBounds, { type -> type.getJetTypeFqName(printTypeArguments) }, "&")
     }