diff --git a/compiler/fir/fir2ir/src/org/jetbrains/kotlin/fir/backend/Fir2IrClassifierStorage.kt b/compiler/fir/fir2ir/src/org/jetbrains/kotlin/fir/backend/Fir2IrClassifierStorage.kt
index 25a3a47d044..1ff087177db 100644
--- a/compiler/fir/fir2ir/src/org/jetbrains/kotlin/fir/backend/Fir2IrClassifierStorage.kt
+++ b/compiler/fir/fir2ir/src/org/jetbrains/kotlin/fir/backend/Fir2IrClassifierStorage.kt
@@ -19,6 +19,8 @@ import org.jetbrains.kotlin.fir.resolve.toSymbol
 import org.jetbrains.kotlin.fir.symbols.ConeClassLikeLookupTag
 import org.jetbrains.kotlin.fir.symbols.impl.FirClassSymbol
 import org.jetbrains.kotlin.fir.symbols.impl.FirTypeParameterSymbol
+import org.jetbrains.kotlin.fir.symbols.lazyResolveToPhase
+import org.jetbrains.kotlin.fir.symbols.lazyResolveToPhaseWithCallableMembers
 import org.jetbrains.kotlin.fir.types.FirTypeRef
 import org.jetbrains.kotlin.fir.types.toLookupTag
 import org.jetbrains.kotlin.ir.UNDEFINED_OFFSET
@@ -30,6 +32,7 @@ import org.jetbrains.kotlin.ir.symbols.IrTypeParameterSymbol
 import org.jetbrains.kotlin.ir.symbols.impl.IrFieldSymbolImpl
 import org.jetbrains.kotlin.ir.symbols.impl.IrTypeParameterSymbolImpl
 import org.jetbrains.kotlin.ir.types.IrType
+import org.jetbrains.kotlin.name.ClassId
 import org.jetbrains.kotlin.name.Name
 import org.jetbrains.kotlin.name.SpecialNames
 import org.jetbrains.kotlin.name.StandardClassIds
@@ -68,9 +71,19 @@ class Fir2IrClassifierStorage(
 
     @OptIn(IrSymbolInternals::class)
     fun preCacheBuiltinClasses() {
-        for ((classId, irBuiltinSymbol) in typeConverter.classIdToSymbolMap) {
+        fun getResolvedClass(classId: ClassId): FirRegularClass? {
             // toSymbol() can return null when using an old stdlib that's missing some types
-            val firClass = classId.toSymbol(session)?.fir as FirRegularClass? ?: continue
+            val firClass = classId.toSymbol(session)?.fir as FirRegularClass? ?: return null
+
+            // Built-in classes may come from sources in the Kotlin project, and so have unresolved types in signatures.
+            // Still, we need return types for all members to make a list of 'IrDeclarations'. Also see 'Fir2IrLazyClass.declarations'.
+            firClass.lazyResolveToPhaseWithCallableMembers(FirResolvePhase.IMPLICIT_TYPES_BODY_RESOLVE)
+
+            return firClass
+        }
+
+        for ((classId, irBuiltinSymbol) in typeConverter.classIdToSymbolMap) {
+            val firClass = getResolvedClass(classId) ?: continue
             val irClass = irBuiltinSymbol.owner
             classCache[firClass] = irClass
             classifiersGenerator.processClassHeader(firClass, irClass)
@@ -78,7 +91,7 @@ class Fir2IrClassifierStorage(
         }
         for ((primitiveClassId, primitiveArrayId) in StandardClassIds.primitiveArrayTypeByElementType) {
             // toSymbol() can return null when using an old stdlib that's missing some types
-            val firClass = primitiveArrayId.toLookupTag().toSymbol(session)?.fir as FirRegularClass? ?: continue
+            val firClass = getResolvedClass(primitiveArrayId) ?: continue
             val irType = typeConverter.classIdToTypeMap[primitiveClassId]
             val irClass = irBuiltIns.primitiveArrayForType[irType]!!.owner
             classCache[firClass] = irClass
diff --git a/compiler/fir/fir2ir/src/org/jetbrains/kotlin/fir/backend/IrBuiltInsOverFir.kt b/compiler/fir/fir2ir/src/org/jetbrains/kotlin/fir/backend/IrBuiltInsOverFir.kt
index 7393a25c94d..bdfef1b9dc1 100644
--- a/compiler/fir/fir2ir/src/org/jetbrains/kotlin/fir/backend/IrBuiltInsOverFir.kt
+++ b/compiler/fir/fir2ir/src/org/jetbrains/kotlin/fir/backend/IrBuiltInsOverFir.kt
@@ -12,13 +12,16 @@ import org.jetbrains.kotlin.config.LanguageVersionSettings
 import org.jetbrains.kotlin.descriptors.Modality
 import org.jetbrains.kotlin.fir.FirSession
 import org.jetbrains.kotlin.fir.containingClassLookupTag
+import org.jetbrains.kotlin.fir.declarations.FirResolvePhase
 import org.jetbrains.kotlin.fir.descriptors.FirModuleDescriptor
 import org.jetbrains.kotlin.fir.resolve.providers.FirSymbolProvider
 import org.jetbrains.kotlin.fir.resolve.providers.symbolProvider
 import org.jetbrains.kotlin.fir.scopes.getFunctions
 import org.jetbrains.kotlin.fir.symbols.impl.FirCallableSymbol
 import org.jetbrains.kotlin.fir.symbols.impl.FirNamedFunctionSymbol
+import org.jetbrains.kotlin.fir.symbols.impl.FirPropertySymbol
 import org.jetbrains.kotlin.fir.symbols.impl.FirRegularClassSymbol
+import org.jetbrains.kotlin.fir.symbols.lazyResolveToPhase
 import org.jetbrains.kotlin.fir.types.*
 import org.jetbrains.kotlin.ir.BuiltInOperatorNames
 import org.jetbrains.kotlin.ir.IrBuiltIns
@@ -655,15 +658,21 @@ class IrBuiltInsOverFir(
     }
 
     private fun findFunction(functionSymbol: FirNamedFunctionSymbol): IrSimpleFunctionSymbol {
+        functionSymbol.lazyResolveToPhase(FirResolvePhase.IMPLICIT_TYPES_BODY_RESOLVE)
+
         val irParent = findIrParent(functionSymbol)
         return components.declarationStorage.getOrCreateIrFunction(functionSymbol.fir, irParent).symbol
     }
 
     private fun findProperties(packageName: FqName, name: Name): List<IrPropertySymbol> {
-        return symbolProvider.getTopLevelPropertySymbols(packageName, name).map { firOpSymbol ->
-            val irParent = findIrParent(firOpSymbol)
-            components.declarationStorage.getOrCreateIrProperty(firOpSymbol.fir, irParent).symbol
-        }
+        return symbolProvider.getTopLevelPropertySymbols(packageName, name).map { findProperty(it) }
+    }
+
+    private fun findProperty(propertySymbol: FirPropertySymbol): IrPropertySymbol {
+        propertySymbol.lazyResolveToPhase(FirResolvePhase.IMPLICIT_TYPES_BODY_RESOLVE)
+
+        val irParent = findIrParent(propertySymbol)
+        return components.declarationStorage.getOrCreateIrProperty(propertySymbol.fir, irParent).symbol
     }
 
     private fun findIrParent(firSymbol: FirCallableSymbol<*>): IrDeclarationParent? {