diff --git a/compiler/ir/backend.js/src/org/jetbrains/kotlin/ir/backend/js/lower/VarargLowering.kt b/compiler/ir/backend.js/src/org/jetbrains/kotlin/ir/backend/js/lower/VarargLowering.kt
index a837107b102..2fe6c6722c4 100644
--- a/compiler/ir/backend.js/src/org/jetbrains/kotlin/ir/backend/js/lower/VarargLowering.kt
+++ b/compiler/ir/backend.js/src/org/jetbrains/kotlin/ir/backend/js/lower/VarargLowering.kt
@@ -20,10 +20,7 @@ import org.jetbrains.kotlin.ir.expressions.impl.IrVarargImpl
 import org.jetbrains.kotlin.ir.types.IrType
 import org.jetbrains.kotlin.ir.types.classifierOrNull
 import org.jetbrains.kotlin.ir.types.impl.IrSimpleTypeImpl
-import org.jetbrains.kotlin.ir.util.constructors
-import org.jetbrains.kotlin.ir.util.defaultType
-import org.jetbrains.kotlin.ir.util.getInlineClassBackingField
-import org.jetbrains.kotlin.ir.util.getInlinedClass
+import org.jetbrains.kotlin.ir.util.*
 import org.jetbrains.kotlin.ir.visitors.IrElementTransformerVoid
 import org.jetbrains.kotlin.ir.visitors.transformChildrenVoid
 
@@ -86,8 +83,8 @@ private class VarargTransformer(
         val needUnboxing: Boolean
         val arrayInlineClass = expression.type.getInlinedClass()
         if (arrayInlineClass != null) {
-            primitiveElementType = getInlineClassBackingField(elementType.getInlinedClass()!!).type
-            primitiveExpressionType = getInlineClassBackingField(arrayInlineClass).type
+            primitiveElementType = getInlineClassUnderlyingType(elementType.getInlinedClass()!!)
+            primitiveExpressionType = getInlineClassUnderlyingType(arrayInlineClass)
             needUnboxing = true
         } else {
             primitiveElementType = elementType
diff --git a/compiler/ir/ir.tree/src/org/jetbrains/kotlin/ir/util/InlineClasses.kt b/compiler/ir/ir.tree/src/org/jetbrains/kotlin/ir/util/InlineClasses.kt
index 1f3e888e3a7..6d85547a694 100644
--- a/compiler/ir/ir.tree/src/org/jetbrains/kotlin/ir/util/InlineClasses.kt
+++ b/compiler/ir/ir.tree/src/org/jetbrains/kotlin/ir/util/InlineClasses.kt
@@ -6,6 +6,7 @@
 package org.jetbrains.kotlin.ir.util
 
 import org.jetbrains.kotlin.ir.declarations.IrClass
+import org.jetbrains.kotlin.ir.declarations.IrConstructor
 import org.jetbrains.kotlin.ir.declarations.IrField
 import org.jetbrains.kotlin.ir.declarations.IrProperty
 import org.jetbrains.kotlin.ir.symbols.IrClassSymbol
@@ -28,7 +29,7 @@ fun IrType.getInlinedClass(): IrClass? {
                 var fieldType: IrType
                 var fieldInlinedClass = erased
                 while (true) {
-                    fieldType = getInlineClassBackingField(fieldInlinedClass).type
+                    fieldType = getInlineClassUnderlyingType(fieldInlinedClass)
                     if (fieldType.isMarkedNullable()) {
                         return null
                     }
@@ -55,6 +56,15 @@ private tailrec fun erase(type: IrType): IrClass? {
     }
 }
 
+fun getInlineClassUnderlyingType(irClass: IrClass): IrType {
+    for (declaration in irClass.declarations) {
+        if (declaration is IrConstructor && declaration.isPrimary) {
+            return declaration.valueParameters[0].type
+        }
+    }
+    error("Inline class has no primary constructor: ${irClass.fqNameWhenAvailable}")
+}
+
 fun getInlineClassBackingField(irClass: IrClass): IrField {
     for (declaration in irClass.declarations) {
         if (declaration is IrField)
@@ -63,5 +73,5 @@ fun getInlineClassBackingField(irClass: IrClass): IrField {
         if (declaration is IrProperty)
             return declaration.backingField ?: continue
     }
-    error("Inline class has no field")
+    error("Inline class has no field: ${irClass.fqNameWhenAvailable}")
 }