diff --git a/core/descriptors.jvm/src/org/jetbrains/kotlin/load/kotlin/inlineClassMapping.kt b/core/descriptors.jvm/src/org/jetbrains/kotlin/load/kotlin/inlineClassMapping.kt
index 382308fda46..1f8509d299b 100644
--- a/core/descriptors.jvm/src/org/jetbrains/kotlin/load/kotlin/inlineClassMapping.kt
+++ b/core/descriptors.jvm/src/org/jetbrains/kotlin/load/kotlin/inlineClassMapping.kt
@@ -6,15 +6,15 @@
 package org.jetbrains.kotlin.load.kotlin
 
 import org.jetbrains.kotlin.builtins.KotlinBuiltIns
-import org.jetbrains.kotlin.descriptors.ClassDescriptor
-import org.jetbrains.kotlin.descriptors.ClassifierDescriptor
 import org.jetbrains.kotlin.descriptors.TypeParameterDescriptor
 import org.jetbrains.kotlin.resolve.substitutedUnderlyingType
 import org.jetbrains.kotlin.resolve.unsubstitutedUnderlyingType
 import org.jetbrains.kotlin.types.KotlinType
+import org.jetbrains.kotlin.types.TypeSystemCommonBackendContext
 import org.jetbrains.kotlin.types.TypeUtils
-import org.jetbrains.kotlin.types.isNullable
-import org.jetbrains.kotlin.types.typeUtil.makeNullable
+import org.jetbrains.kotlin.types.model.KotlinTypeMarker
+import org.jetbrains.kotlin.types.model.SimpleTypeMarker
+import org.jetbrains.kotlin.types.model.TypeConstructorMarker
 import org.jetbrains.kotlin.types.typeUtil.representativeUpperBound
 
 internal fun computeUnderlyingType(inlineClassType: KotlinType): KotlinType? {
@@ -27,39 +27,42 @@ internal fun computeUnderlyingType(inlineClassType: KotlinType): KotlinType? {
         inlineClassType.substitutedUnderlyingType()
 }
 
-internal fun computeExpandedTypeForInlineClass(inlineClassType: KotlinType): KotlinType? =
+fun TypeSystemCommonBackendContext.computeExpandedTypeForInlineClass(inlineClassType: KotlinTypeMarker): KotlinTypeMarker? =
     computeExpandedTypeInner(inlineClassType, hashSetOf())
 
-private fun computeExpandedTypeInner(kotlinType: KotlinType, visitedClassifiers: HashSet<ClassifierDescriptor>): KotlinType? {
-    val classifier = kotlinType.constructor.declarationDescriptor
-        ?: throw AssertionError("Type with a declaration expected: $kotlinType")
+private fun TypeSystemCommonBackendContext.computeExpandedTypeInner(
+    kotlinType: KotlinTypeMarker, visitedClassifiers: HashSet<TypeConstructorMarker>
+): KotlinTypeMarker? {
+    val classifier = kotlinType.typeConstructor()
     if (!visitedClassifiers.add(classifier)) return null
 
+    val typeParameter = classifier.getTypeParameterClassifier()
+
     return when {
-        classifier is TypeParameterDescriptor ->
-            computeExpandedTypeInner(classifier.representativeUpperBound, visitedClassifiers)
+        typeParameter != null ->
+            computeExpandedTypeInner(typeParameter.getRepresentativeUpperBound(), visitedClassifiers)
                 ?.let { expandedUpperBound ->
-                    if (expandedUpperBound.isNullable() || !kotlinType.isMarkedNullable)
+                    if (expandedUpperBound.isNullableType() || !kotlinType.isMarkedNullable())
                         expandedUpperBound
                     else
                         expandedUpperBound.makeNullable()
                 }
 
-        classifier is ClassDescriptor && classifier.isInline -> {
+        classifier.isInlineClass() -> {
             // kotlinType is the boxed inline class type
 
-            val underlyingType = kotlinType.substitutedUnderlyingType() ?: return null
+            val underlyingType = kotlinType.getSubstitutedUnderlyingType() ?: return null
             val expandedUnderlyingType = computeExpandedTypeInner(underlyingType, visitedClassifiers) ?: return null
             when {
-                !kotlinType.isNullable() -> expandedUnderlyingType
+                !kotlinType.isNullableType() -> expandedUnderlyingType
 
                 // Here inline class type is nullable. Apply nullability to the expandedUnderlyingType.
 
                 // Nullable types become inline class boxes
-                expandedUnderlyingType.isNullable() -> kotlinType
+                expandedUnderlyingType.isNullableType() -> kotlinType
 
                 // Primitives become inline class boxes
-                KotlinBuiltIns.isPrimitiveType(expandedUnderlyingType) -> kotlinType
+                expandedUnderlyingType is SimpleTypeMarker && expandedUnderlyingType.isPrimitiveType() -> kotlinType
 
                 // Non-null reference types become nullable reference types
                 else -> expandedUnderlyingType.makeNullable()
diff --git a/core/descriptors.jvm/src/org/jetbrains/kotlin/load/kotlin/typeSignatureMapping.kt b/core/descriptors.jvm/src/org/jetbrains/kotlin/load/kotlin/typeSignatureMapping.kt
index 4d2aef07e83..532e0a676e9 100644
--- a/core/descriptors.jvm/src/org/jetbrains/kotlin/load/kotlin/typeSignatureMapping.kt
+++ b/core/descriptors.jvm/src/org/jetbrains/kotlin/load/kotlin/typeSignatureMapping.kt
@@ -17,6 +17,7 @@ import org.jetbrains.kotlin.resolve.descriptorUtil.fqNameUnsafe
 import org.jetbrains.kotlin.resolve.jvm.JvmClassName
 import org.jetbrains.kotlin.resolve.jvm.JvmPrimitiveType
 import org.jetbrains.kotlin.types.*
+import org.jetbrains.kotlin.types.checker.SimpleClassicTypeSystemContext
 import org.jetbrains.kotlin.types.typeUtil.replaceArgumentsWithStarProjections
 import org.jetbrains.kotlin.types.typeUtil.representativeUpperBound
 import org.jetbrains.kotlin.utils.DO_NOTHING_3
@@ -136,7 +137,7 @@ fun <T : Any> mapType(
         descriptor is ClassDescriptor -> {
             // NB if inline class is recursive, it's ok to map it as wrapped
             if (descriptor.isInline && !mode.needInlineClassWrapping) {
-                val expandedType = computeExpandedTypeForInlineClass(kotlinType)
+                val expandedType = SimpleClassicTypeSystemContext.computeExpandedTypeForInlineClass(kotlinType) as KotlinType?
                 if (expandedType != null) {
                     return mapType(
                         expandedType,
diff --git a/core/descriptors/src/org/jetbrains/kotlin/types/TypeSystemCommonBackendContext.kt b/core/descriptors/src/org/jetbrains/kotlin/types/TypeSystemCommonBackendContext.kt
index d432711796f..4ce26d7c58c 100644
--- a/core/descriptors/src/org/jetbrains/kotlin/types/TypeSystemCommonBackendContext.kt
+++ b/core/descriptors/src/org/jetbrains/kotlin/types/TypeSystemCommonBackendContext.kt
@@ -6,9 +6,7 @@
 package org.jetbrains.kotlin.types
 
 import org.jetbrains.kotlin.name.FqName
-import org.jetbrains.kotlin.types.model.KotlinTypeMarker
-import org.jetbrains.kotlin.types.model.TypeConstructorMarker
-import org.jetbrains.kotlin.types.model.TypeSystemContext
+import org.jetbrains.kotlin.types.model.*
 
 interface TypeSystemCommonBackendContext : TypeSystemContext {
     fun TypeConstructorMarker.isFinalClassOrEnumEntryOrAnnotationClassConstructor(): Boolean
@@ -24,4 +22,15 @@ interface TypeSystemCommonBackendContext : TypeSystemContext {
      * TODO: provide a more granular & elaborate API here to reduce confusion
      */
     fun KotlinTypeMarker.getAnnotationFirstArgumentValue(fqName: FqName): Any?
+
+    fun TypeConstructorMarker.getTypeParameterClassifier(): TypeParameterMarker?
+    fun TypeConstructorMarker.isInlineClass(): Boolean
+    fun TypeParameterMarker.getRepresentativeUpperBound(): KotlinTypeMarker
+    fun KotlinTypeMarker.getSubstitutedUnderlyingType(): KotlinTypeMarker?
+
+    fun KotlinTypeMarker.isMarkedNullable(): Boolean =
+        this is SimpleTypeMarker && isMarkedNullable()
+
+    fun KotlinTypeMarker.makeNullable(): KotlinTypeMarker =
+        asSimpleType()?.withNullability(true) ?: this
 }
diff --git a/core/descriptors/src/org/jetbrains/kotlin/types/checker/ClassicTypeSystemContext.kt b/core/descriptors/src/org/jetbrains/kotlin/types/checker/ClassicTypeSystemContext.kt
index ab8b9d2dfe6..ff2d68fcb8f 100644
--- a/core/descriptors/src/org/jetbrains/kotlin/types/checker/ClassicTypeSystemContext.kt
+++ b/core/descriptors/src/org/jetbrains/kotlin/types/checker/ClassicTypeSystemContext.kt
@@ -16,10 +16,12 @@ import org.jetbrains.kotlin.resolve.constants.IntegerLiteralTypeConstructor
 import org.jetbrains.kotlin.resolve.descriptorUtil.hasExactAnnotation
 import org.jetbrains.kotlin.resolve.descriptorUtil.hasNoInferAnnotation
 import org.jetbrains.kotlin.resolve.descriptorUtil.isExactAnnotation
+import org.jetbrains.kotlin.resolve.substitutedUnderlyingType
 import org.jetbrains.kotlin.types.*
 import org.jetbrains.kotlin.types.model.*
 import org.jetbrains.kotlin.types.typeUtil.asTypeProjection
 import org.jetbrains.kotlin.types.typeUtil.contains
+import org.jetbrains.kotlin.types.typeUtil.representativeUpperBound
 import kotlin.contracts.ExperimentalContracts
 import kotlin.contracts.contract
 
@@ -495,6 +497,26 @@ interface ClassicTypeSystemContext : TypeSystemInferenceExtensionContext, TypeSy
         require(this is KotlinType, this::errorMessage)
         return annotations.findAnnotation(fqName)?.allValueArguments?.values?.firstOrNull()?.value
     }
+
+    override fun TypeConstructorMarker.getTypeParameterClassifier(): TypeParameterMarker? {
+        require(this is TypeConstructor, this::errorMessage)
+        return declarationDescriptor as? TypeParameterDescriptor
+    }
+
+    override fun TypeConstructorMarker.isInlineClass(): Boolean {
+        require(this is TypeConstructor, this::errorMessage)
+        return (declarationDescriptor as? ClassDescriptor)?.isInline == true
+    }
+
+    override fun TypeParameterMarker.getRepresentativeUpperBound(): KotlinTypeMarker {
+        require(this is TypeParameterDescriptor, this::errorMessage)
+        return representativeUpperBound
+    }
+
+    override fun KotlinTypeMarker.getSubstitutedUnderlyingType(): KotlinTypeMarker? {
+        require(this is KotlinType, this::errorMessage)
+        return substitutedUnderlyingType()
+    }
 }
 
 fun TypeVariance.convertVariance(): Variance {