diff --git a/compiler/fir/tree/src/org/jetbrains/kotlin/fir/declarations/utils/FirDeclarationBuildingUtils.kt b/compiler/fir/tree/src/org/jetbrains/kotlin/fir/declarations/utils/FirDeclarationBuildingUtils.kt
index 2d6616b0bf8..d54408c1797 100644
--- a/compiler/fir/tree/src/org/jetbrains/kotlin/fir/declarations/utils/FirDeclarationBuildingUtils.kt
+++ b/compiler/fir/tree/src/org/jetbrains/kotlin/fir/declarations/utils/FirDeclarationBuildingUtils.kt
@@ -6,12 +6,8 @@
 package org.jetbrains.kotlin.fir.declarations.utils
 
 import org.jetbrains.kotlin.fir.declarations.FirDeclaration
-import org.jetbrains.kotlin.fir.declarations.FirFile
-import org.jetbrains.kotlin.fir.declarations.FirRegularClass
 import org.jetbrains.kotlin.fir.declarations.builder.FirRegularClassBuilder
 import org.jetbrains.kotlin.fir.declarations.builder.FirTypeParameterBuilder
-import org.jetbrains.kotlin.fir.declarations.impl.FirFileImpl
-import org.jetbrains.kotlin.fir.declarations.impl.FirRegularClassImpl
 
 fun FirTypeParameterBuilder.addDefaultBoundIfNecessary() {
     if (bounds.isEmpty()) {
@@ -26,16 +22,3 @@ fun FirRegularClassBuilder.addDeclaration(declaration: FirDeclaration) {
 fun FirRegularClassBuilder.addDeclarations(declarations: Collection<FirDeclaration>) {
     declarations.forEach(this::addDeclaration)
 }
-
-fun FirFile.addDeclaration(declaration: FirDeclaration) {
-    require(this is FirFileImpl)
-    declarations += declaration
-}
-
-fun FirRegularClass.addDeclaration(declaration: FirDeclaration) {
-    @Suppress("LiftReturnOrAssignment")
-    when (this) {
-        is FirRegularClassImpl -> declarations += declaration
-        else -> throw IllegalStateException()
-    }
-}