diff --git a/compiler/fir/resolve/src/org/jetbrains/kotlin/fir/resolve/SupertypeUtils.kt b/compiler/fir/resolve/src/org/jetbrains/kotlin/fir/resolve/SupertypeUtils.kt
index 513b82eb4a1..93ec02d5c42 100644
--- a/compiler/fir/resolve/src/org/jetbrains/kotlin/fir/resolve/SupertypeUtils.kt
+++ b/compiler/fir/resolve/src/org/jetbrains/kotlin/fir/resolve/SupertypeUtils.kt
@@ -13,11 +13,11 @@ import org.jetbrains.kotlin.fir.scopes.impl.*
 import org.jetbrains.kotlin.fir.symbols.impl.*
 import org.jetbrains.kotlin.fir.types.*
 
-interface SupertypeSupplier {
-    fun forClass(firClass: FirClass<*>): List<ConeClassLikeType>
-    fun expansionForTypeAlias(typeAlias: FirTypeAlias): ConeClassLikeType?
+abstract class SupertypeSupplier {
+    abstract fun forClass(firClass: FirClass<*>): List<ConeClassLikeType>
+    abstract fun expansionForTypeAlias(typeAlias: FirTypeAlias): ConeClassLikeType?
 
-    object Default : SupertypeSupplier {
+    object Default : SupertypeSupplier() {
         override fun forClass(firClass: FirClass<*>) = firClass.superConeTypes
         override fun expansionForTypeAlias(typeAlias: FirTypeAlias) = typeAlias.expandedConeType
     }
diff --git a/compiler/fir/resolve/src/org/jetbrains/kotlin/fir/resolve/transformers/FirSupertypesResolution.kt b/compiler/fir/resolve/src/org/jetbrains/kotlin/fir/resolve/transformers/FirSupertypesResolution.kt
index 0d404e293e7..f56da95ff50 100644
--- a/compiler/fir/resolve/src/org/jetbrains/kotlin/fir/resolve/transformers/FirSupertypesResolution.kt
+++ b/compiler/fir/resolve/src/org/jetbrains/kotlin/fir/resolve/transformers/FirSupertypesResolution.kt
@@ -271,7 +271,7 @@ private class SupertypeComputationSession {
     private val scopesForNestedClassesMap = hashMapOf<FirRegularClass, FirImmutableCompositeScope>()
     private val supertypeStatusMap = linkedMapOf<FirClassLikeDeclaration<*>, SupertypeComputationStatus>()
 
-    val supertypesSupplier = object : SupertypeSupplier {
+    val supertypesSupplier = object : SupertypeSupplier() {
         override fun forClass(firClass: FirClass<*>): List<ConeClassLikeType> {
             if (firClass.resolvePhase > FirResolvePhase.SUPER_TYPES) return firClass.superConeTypes
             return (getSupertypesComputationStatus(firClass) as? SupertypeComputationStatus.Computed)?.supertypeRefs?.mapNotNull {