diff --git a/compiler/ir/backend.common/src/org/jetbrains/kotlin/backend/common/ir/Ir.kt b/compiler/ir/backend.common/src/org/jetbrains/kotlin/backend/common/ir/Ir.kt
index af8b8240831..fab1a62e650 100644
--- a/compiler/ir/backend.common/src/org/jetbrains/kotlin/backend/common/ir/Ir.kt
+++ b/compiler/ir/backend.common/src/org/jetbrains/kotlin/backend/common/ir/Ir.kt
@@ -19,8 +19,12 @@ import org.jetbrains.kotlin.ir.declarations.IrPackageFragment
 import org.jetbrains.kotlin.ir.symbols.IrClassSymbol
 import org.jetbrains.kotlin.ir.symbols.IrFunctionSymbol
 import org.jetbrains.kotlin.ir.symbols.IrSimpleFunctionSymbol
+import org.jetbrains.kotlin.ir.types.IrType
 import org.jetbrains.kotlin.ir.types.classOrNull
-import org.jetbrains.kotlin.ir.util.*
+import org.jetbrains.kotlin.ir.util.ReferenceSymbolTable
+import org.jetbrains.kotlin.ir.util.fqNameWhenAvailable
+import org.jetbrains.kotlin.ir.util.getPackageFragment
+import org.jetbrains.kotlin.ir.util.referenceFunction
 import org.jetbrains.kotlin.name.FqName
 import org.jetbrains.kotlin.name.Name
 import org.jetbrains.kotlin.resolve.calls.components.isVararg
@@ -34,6 +38,10 @@ abstract class Ir<out T : CommonBackendContext>(val context: T, val irModule: Ir
 
     val defaultParameterDeclarationsCache = mutableMapOf<IrFunction, IrFunction>()
 
+    // If irType is an inline class type, return the underlying type according to the
+    // unfolding rules of the current backend. Otherwise, returns null.
+    open fun unfoldInlineClassType(irType: IrType): IrType? = null
+
     open fun shouldGenerateHandlerParameterForDefaultBodyFun() = false
 }
 
diff --git a/compiler/ir/backend.common/src/org/jetbrains/kotlin/backend/common/ir/IrUtils.kt b/compiler/ir/backend.common/src/org/jetbrains/kotlin/backend/common/ir/IrUtils.kt
index c9d70d55624..451c3460358 100644
--- a/compiler/ir/backend.common/src/org/jetbrains/kotlin/backend/common/ir/IrUtils.kt
+++ b/compiler/ir/backend.common/src/org/jetbrains/kotlin/backend/common/ir/IrUtils.kt
@@ -565,7 +565,3 @@ fun copyBodyToStatic(oldFunction: IrFunction, staticFunction: IrFunction) {
             ?.transform(VariableRemapper(mapping), null)
             ?.patchDeclarationParents(staticFunction)
 }
-
-fun IrClass.underlyingType() = if (isInline)
-    constructors.single { it.isPrimary }.valueParameters[0].type
-else defaultType
diff --git a/compiler/ir/backend.common/src/org/jetbrains/kotlin/backend/common/lower/DefaultArgumentStubGenerator.kt b/compiler/ir/backend.common/src/org/jetbrains/kotlin/backend/common/lower/DefaultArgumentStubGenerator.kt
index 1dac5146e23..1252c57e808 100644
--- a/compiler/ir/backend.common/src/org/jetbrains/kotlin/backend/common/lower/DefaultArgumentStubGenerator.kt
+++ b/compiler/ir/backend.common/src/org/jetbrains/kotlin/backend/common/lower/DefaultArgumentStubGenerator.kt
@@ -6,21 +6,21 @@
 package org.jetbrains.kotlin.backend.common.lower
 
 import org.jetbrains.kotlin.backend.common.*
-import org.jetbrains.kotlin.backend.common.descriptors.*
+import org.jetbrains.kotlin.backend.common.descriptors.WrappedClassConstructorDescriptor
+import org.jetbrains.kotlin.backend.common.descriptors.WrappedValueParameterDescriptor
+import org.jetbrains.kotlin.backend.common.descriptors.synthesizedName
+import org.jetbrains.kotlin.backend.common.descriptors.wrappedSimpleFunctionDescriptorBasedOn
 import org.jetbrains.kotlin.backend.common.ir.*
 import org.jetbrains.kotlin.descriptors.Modality
 import org.jetbrains.kotlin.descriptors.SimpleFunctionDescriptor
-import org.jetbrains.kotlin.ir.IrElement
 import org.jetbrains.kotlin.ir.UNDEFINED_OFFSET
 import org.jetbrains.kotlin.ir.builders.*
 import org.jetbrains.kotlin.ir.declarations.*
 import org.jetbrains.kotlin.ir.declarations.impl.IrConstructorImpl
 import org.jetbrains.kotlin.ir.declarations.impl.IrFunctionImpl
 import org.jetbrains.kotlin.ir.declarations.impl.IrValueParameterImpl
-import org.jetbrains.kotlin.ir.descriptors.IrBuiltIns
 import org.jetbrains.kotlin.ir.expressions.*
 import org.jetbrains.kotlin.ir.expressions.impl.*
-import org.jetbrains.kotlin.ir.symbols.IrClassSymbol
 import org.jetbrains.kotlin.ir.symbols.IrConstructorSymbol
 import org.jetbrains.kotlin.ir.symbols.IrFunctionSymbol
 import org.jetbrains.kotlin.ir.symbols.impl.IrConstructorSymbolImpl
@@ -31,7 +31,6 @@ import org.jetbrains.kotlin.ir.util.*
 import org.jetbrains.kotlin.ir.visitors.IrElementTransformerVoid
 import org.jetbrains.kotlin.ir.visitors.transformChildrenVoid
 import org.jetbrains.kotlin.name.Name
-import org.jetbrains.kotlin.utils.addToStdlib.safeAs
 
 // TODO: fix expect/actual default parameters
 
@@ -347,11 +346,7 @@ open class DefaultParameterInjector(
                 maskValues[maskIndex] = maskValues[maskIndex] or (1 shl (argIndex % 32))
             }
             val valueParameterDeclaration = realFunction.valueParameters[argIndex]
-            val defaultValueArgument = if (valueParameterDeclaration.varargElementType != null) {
-                null
-            } else {
-                nullConst(expression, realFunction.valueParameters[argIndex].type)
-            }
+            val defaultValueArgument = nullConst(expression.startOffset, expression.endOffset, valueParameterDeclaration)
             valueParameterDeclaration to (valueArgument ?: defaultValueArgument)
         }
 
@@ -387,16 +382,23 @@ open class DefaultParameterInjector(
         return result
     }
 
-    protected open fun nullConst(expression: IrElement, type: IrType): IrExpression = when {
-        type.isFloat() -> IrConstImpl.float(expression.startOffset, expression.endOffset, type, 0.0F)
-        type.isDouble() -> IrConstImpl.double(expression.startOffset, expression.endOffset, type, 0.0)
-        type.isBoolean() -> IrConstImpl.boolean(expression.startOffset, expression.endOffset, type, false)
-        type.isByte() -> IrConstImpl.byte(expression.startOffset, expression.endOffset, type, 0)
-        type.isChar() -> IrConstImpl.char(expression.startOffset, expression.endOffset, type, 0.toChar())
-        type.isShort() -> IrConstImpl.short(expression.startOffset, expression.endOffset, type, 0)
-        type.isInt() -> IrConstImpl.int(expression.startOffset, expression.endOffset, type, 0)
-        type.isLong() -> IrConstImpl.long(expression.startOffset, expression.endOffset, type, 0)
-        else -> IrConstImpl.constNull(expression.startOffset, expression.endOffset, context.irBuiltIns.nothingNType)
+    protected open fun nullConst(startOffset: Int, endOffset: Int, irParameter: IrValueParameter): IrExpression? =
+        if (irParameter.varargElementType != null) {
+            null
+        } else {
+            nullConst(startOffset, endOffset, irParameter.type)
+        }
+
+    protected open fun nullConst(startOffset: Int, endOffset: Int, type: IrType): IrExpression = when {
+        type.isFloat() -> IrConstImpl.float(startOffset, endOffset, type, 0.0F)
+        type.isDouble() -> IrConstImpl.double(startOffset, endOffset, type, 0.0)
+        type.isBoolean() -> IrConstImpl.boolean(startOffset, endOffset, type, false)
+        type.isByte() -> IrConstImpl.byte(startOffset, endOffset, type, 0)
+        type.isChar() -> IrConstImpl.char(startOffset, endOffset, type, 0.toChar())
+        type.isShort() -> IrConstImpl.short(startOffset, endOffset, type, 0)
+        type.isInt() -> IrConstImpl.int(startOffset, endOffset, type, 0)
+        type.isLong() -> IrConstImpl.long(startOffset, endOffset, type, 0)
+        else -> IrConstImpl.constNull(startOffset, endOffset, context.irBuiltIns.nothingNType)
     }
 
     private fun log(msg: () -> String) = context.log { "DEFAULT-INJECTOR: ${msg()}" }
@@ -449,7 +451,7 @@ private fun IrFunction.generateDefaultsFunctionImpl(
     }
 
     newFunction.copyTypeParametersFrom(this)
-    val newValueParameters = valueParameters.map { it.copyMaybeNullableTo(newFunction, context.irBuiltIns) } + syntheticParameters
+    val newValueParameters = valueParameters.map { it.copyMaybeNullableTo(newFunction, context) } + syntheticParameters
     newValueParameters.forEach {
         it.defaultValue = null
     }
@@ -559,10 +561,10 @@ internal val kConstructorMarkerName = "marker".synthesizedName
 
 private fun parameterMaskName(number: Int) = "mask$number".synthesizedName
 
-private fun IrValueParameter.copyMaybeNullableTo(irFunction: IrFunction, irBuiltIns: IrBuiltIns): IrValueParameter {
+private fun IrValueParameter.copyMaybeNullableTo(irFunction: IrFunction, context: CommonBackendContext): IrValueParameter {
     if (defaultValue == null) return copyTo(irFunction)
-    val underlyingType = type.classOrNull?.owner?.underlyingType() ?: type
-    if (underlyingType in irBuiltIns.primitiveIrTypes) return copyTo(irFunction)
+    val underlyingType = context.ir.unfoldInlineClassType(type) ?: type
+    if (underlyingType in context.irBuiltIns.primitiveIrTypes) return copyTo(irFunction)
 
     val newType = type.remapTypeParameters(
         (parent as IrTypeParametersContainer).classIfConstructor,
diff --git a/compiler/ir/backend.js/src/org/jetbrains/kotlin/ir/backend/js/JsIrBackendContext.kt b/compiler/ir/backend.js/src/org/jetbrains/kotlin/ir/backend/js/JsIrBackendContext.kt
index c3aaba0be5f..255e19e84a5 100644
--- a/compiler/ir/backend.js/src/org/jetbrains/kotlin/ir/backend/js/JsIrBackendContext.kt
+++ b/compiler/ir/backend.js/src/org/jetbrains/kotlin/ir/backend/js/JsIrBackendContext.kt
@@ -29,15 +29,13 @@ import org.jetbrains.kotlin.ir.backend.js.utils.OperatorNames
 import org.jetbrains.kotlin.ir.declarations.*
 import org.jetbrains.kotlin.ir.declarations.impl.IrFileImpl
 import org.jetbrains.kotlin.ir.descriptors.IrBuiltIns
-import org.jetbrains.kotlin.ir.symbols.*
-import org.jetbrains.kotlin.ir.types.IrDynamicType
-import org.jetbrains.kotlin.ir.types.IrSimpleType
-import org.jetbrains.kotlin.ir.types.classifierOrFail
+import org.jetbrains.kotlin.ir.symbols.IrClassSymbol
+import org.jetbrains.kotlin.ir.symbols.IrClassifierSymbol
+import org.jetbrains.kotlin.ir.symbols.IrEnumEntrySymbol
+import org.jetbrains.kotlin.ir.symbols.IrSimpleFunctionSymbol
+import org.jetbrains.kotlin.ir.types.*
 import org.jetbrains.kotlin.ir.types.impl.IrDynamicTypeImpl
-import org.jetbrains.kotlin.ir.util.SymbolTable
-import org.jetbrains.kotlin.ir.util.getPropertyGetter
-import org.jetbrains.kotlin.ir.util.getPropertySetter
-import org.jetbrains.kotlin.ir.util.kotlinPackageFqn
+import org.jetbrains.kotlin.ir.util.*
 import org.jetbrains.kotlin.name.FqName
 import org.jetbrains.kotlin.name.Name
 import org.jetbrains.kotlin.resolve.scopes.MemberScope
@@ -199,6 +197,10 @@ class JsIrBackendContext(
             override val returnIfSuspended = symbolTable.referenceSimpleFunction(getJsInternalFunction("returnIfSuspended"))
         }
 
+        override fun unfoldInlineClassType(irType: IrType): IrType? {
+            return irType.getInlinedClass()?.typeWith()
+        }
+
         override fun shouldGenerateHandlerParameterForDefaultBodyFun() = true
     }
 
diff --git a/compiler/ir/backend.jvm/src/org/jetbrains/kotlin/backend/jvm/JvmBackendContext.kt b/compiler/ir/backend.jvm/src/org/jetbrains/kotlin/backend/jvm/JvmBackendContext.kt
index baef405506e..26a09f2a755 100644
--- a/compiler/ir/backend.jvm/src/org/jetbrains/kotlin/backend/jvm/JvmBackendContext.kt
+++ b/compiler/ir/backend.jvm/src/org/jetbrains/kotlin/backend/jvm/JvmBackendContext.kt
@@ -12,6 +12,7 @@ import org.jetbrains.kotlin.backend.jvm.codegen.IrTypeMapper
 import org.jetbrains.kotlin.backend.jvm.descriptors.JvmDeclarationFactory
 import org.jetbrains.kotlin.backend.jvm.descriptors.JvmSharedVariablesManager
 import org.jetbrains.kotlin.backend.jvm.intrinsics.IrIntrinsicMethods
+import org.jetbrains.kotlin.backend.jvm.lower.inlineclasses.InlineClassAbi
 import org.jetbrains.kotlin.codegen.ClassBuilder
 import org.jetbrains.kotlin.codegen.state.GenerationState
 import org.jetbrains.kotlin.descriptors.ClassDescriptor
@@ -21,6 +22,7 @@ import org.jetbrains.kotlin.ir.declarations.*
 import org.jetbrains.kotlin.ir.descriptors.IrBuiltIns
 import org.jetbrains.kotlin.ir.symbols.IrClassSymbol
 import org.jetbrains.kotlin.ir.symbols.IrFunctionSymbol
+import org.jetbrains.kotlin.ir.types.IrType
 import org.jetbrains.kotlin.ir.util.ReferenceSymbolTable
 import org.jetbrains.kotlin.ir.util.SymbolTable
 import org.jetbrains.kotlin.name.FqName
@@ -95,6 +97,10 @@ class JvmBackendContext(
     ) : Ir<JvmBackendContext>(this, irModuleFragment) {
         override val symbols = JvmSymbols(this@JvmBackendContext, symbolTable, firMode)
 
+        override fun unfoldInlineClassType(irType: IrType): IrType? {
+            return InlineClassAbi.unboxType(irType)
+        }
+
         override fun shouldGenerateHandlerParameterForDefaultBodyFun() = true
     }
 }
diff --git a/compiler/ir/backend.jvm/src/org/jetbrains/kotlin/backend/jvm/lower/JvmDefaultParameterInjector.kt b/compiler/ir/backend.jvm/src/org/jetbrains/kotlin/backend/jvm/lower/JvmDefaultParameterInjector.kt
index dc253602d7d..5c5d48466eb 100644
--- a/compiler/ir/backend.jvm/src/org/jetbrains/kotlin/backend/jvm/lower/JvmDefaultParameterInjector.kt
+++ b/compiler/ir/backend.jvm/src/org/jetbrains/kotlin/backend/jvm/lower/JvmDefaultParameterInjector.kt
@@ -5,38 +5,30 @@
 
 package org.jetbrains.kotlin.backend.jvm.lower
 
-import org.jetbrains.kotlin.backend.common.ir.underlyingType
 import org.jetbrains.kotlin.backend.common.lower.DefaultParameterInjector
 import org.jetbrains.kotlin.backend.jvm.JvmBackendContext
-import org.jetbrains.kotlin.ir.IrElement
+import org.jetbrains.kotlin.backend.jvm.lower.inlineclasses.unboxInlineClass
+import org.jetbrains.kotlin.ir.declarations.IrValueParameter
 import org.jetbrains.kotlin.ir.expressions.IrExpression
 import org.jetbrains.kotlin.ir.expressions.impl.IrCallImpl
-import org.jetbrains.kotlin.ir.types.*
+import org.jetbrains.kotlin.ir.types.IrSimpleType
+import org.jetbrains.kotlin.ir.types.IrType
+import org.jetbrains.kotlin.ir.types.classOrNull
 
 class JvmDefaultParameterInjector(context: JvmBackendContext) :
     DefaultParameterInjector(context, skipInline = false, skipExternalMethods = false) {
 
     override val context: JvmBackendContext get() = super.context as JvmBackendContext
 
-    override fun nullConst(expression: IrElement, type: IrType): IrExpression {
-        if (type !is IrSimpleType ||
-            type.hasQuestionMark ||
-            type.classOrNull?.owner?.isInline != true
-        ) {
-            return super.nullConst(expression, type)
-        }
-        val underlyingType = type.classOrNull!!.owner.underlyingType()
-        return IrCallImpl(
-            expression.startOffset, expression.endOffset,
-            type,
-            context.ir.symbols.unsafeCoerceIntrinsicSymbol, context.ir.symbols.unsafeCoerceIntrinsicSymbol.descriptor,
-            typeArgumentsCount = 2,
-            valueArgumentsCount = 1
-        ).apply {
+    override fun nullConst(startOffset: Int, endOffset: Int, type: IrType): IrExpression {
+        if (type !is IrSimpleType || type.hasQuestionMark || type.classOrNull?.owner?.isInline != true)
+            return super.nullConst(startOffset, endOffset, type)
+
+        val underlyingType = type.unboxInlineClass()
+        return IrCallImpl(startOffset, endOffset, type, context.ir.symbols.unsafeCoerceIntrinsicSymbol).apply {
             putTypeArgument(0, underlyingType) // from
             putTypeArgument(1, type) // to
-            putValueArgument(0, super.nullConst(expression, underlyingType))
+            putValueArgument(0, super.nullConst(startOffset, endOffset, underlyingType))
         }
     }
-
-}
\ No newline at end of file
+}
diff --git a/compiler/testData/codegen/bytecodeText/inlineClasses/defaultParametersDontBox.kt b/compiler/testData/codegen/bytecodeText/inlineClasses/defaultParametersDontBox.kt
index 625223c486f..fceef113c04 100644
--- a/compiler/testData/codegen/bytecodeText/inlineClasses/defaultParametersDontBox.kt
+++ b/compiler/testData/codegen/bytecodeText/inlineClasses/defaultParametersDontBox.kt
@@ -1,5 +1,4 @@
 // LANGUAGE: +InlineClasses
-// IGNORE_BACKEND: JVM_IR
 // FILE: classes.kt
 
 inline class A(val i: Int)