diff --git a/compiler/fir/psi2fir/src/org/jetbrains/kotlin/fir/builder/BaseFirBuilder.kt b/compiler/fir/psi2fir/src/org/jetbrains/kotlin/fir/builder/BaseFirBuilder.kt
index 9e5a9b7f412..344173c1ce3 100644
--- a/compiler/fir/psi2fir/src/org/jetbrains/kotlin/fir/builder/BaseFirBuilder.kt
+++ b/compiler/fir/psi2fir/src/org/jetbrains/kotlin/fir/builder/BaseFirBuilder.kt
@@ -484,7 +484,7 @@ abstract class BaseFirBuilder<T>(val baseSession: FirSession, val context: Conte
                 rValue = value
                 this.operation = operation
                 indexes += firArrayAccess.arguments
-                argumentList = FirArraySetArgumentList(rValue, indexes)
+                argumentList = buildArraySetArgumentList(rValue, indexes)
             }
             val arrayExpression = this.getChildNodeByType(REFERENCE_EXPRESSION)
             if (arrayExpression != null) {
diff --git a/compiler/fir/resolve/src/org/jetbrains/kotlin/fir/resolve/transformers/FirCallCompletionResultsWriterTransformer.kt b/compiler/fir/resolve/src/org/jetbrains/kotlin/fir/resolve/transformers/FirCallCompletionResultsWriterTransformer.kt
index dbeaf4cd67f..7fe7dfb9918 100644
--- a/compiler/fir/resolve/src/org/jetbrains/kotlin/fir/resolve/transformers/FirCallCompletionResultsWriterTransformer.kt
+++ b/compiler/fir/resolve/src/org/jetbrains/kotlin/fir/resolve/transformers/FirCallCompletionResultsWriterTransformer.kt
@@ -209,7 +209,7 @@ class FirCallCompletionResultsWriterTransformer(
                     }
                 }
                 subCandidate.argumentMapping?.let {
-                    result.replaceArgumentList(FirResolvedArgumentList(it))
+                    result.replaceArgumentList(buildResolvedArgumentList(it))
                 }
                 result.transformExplicitReceiver(integerApproximator, null)
             }
diff --git a/compiler/fir/tree/src/org/jetbrains/kotlin/fir/expressions/FirAbstractArgumentList.kt b/compiler/fir/tree/src/org/jetbrains/kotlin/fir/expressions/FirAbstractArgumentList.kt
new file mode 100644
index 00000000000..7b2ea39ca09
--- /dev/null
+++ b/compiler/fir/tree/src/org/jetbrains/kotlin/fir/expressions/FirAbstractArgumentList.kt
@@ -0,0 +1,28 @@
+/*
+ * Copyright 2010-2020 JetBrains s.r.o. and Kotlin Programming Language contributors.
+ * Use of this source code is governed by the Apache 2.0 license that can be found in the license/LICENSE.txt file.
+ */
+
+package org.jetbrains.kotlin.fir.expressions
+
+import org.jetbrains.kotlin.fir.FirElement
+import org.jetbrains.kotlin.fir.FirSourceElement
+import org.jetbrains.kotlin.fir.visitors.FirTransformer
+import org.jetbrains.kotlin.fir.visitors.FirVisitor
+
+abstract class FirAbstractArgumentList : FirArgumentList() {
+    override val source: FirSourceElement?
+        get() = null
+
+    override fun <D> transformArguments(transformer: FirTransformer<D>, data: D): FirArgumentList {
+        return this
+    }
+
+    override fun <R, D> acceptChildren(visitor: FirVisitor<R, D>, data: D) {
+        // DO NOTHING
+    }
+
+    override fun <D> transformChildren(transformer: FirTransformer<D>, data: D): FirElement {
+        return this
+    }
+}
\ No newline at end of file
diff --git a/compiler/fir/tree/src/org/jetbrains/kotlin/fir/expressions/FirArgumentUtil.kt b/compiler/fir/tree/src/org/jetbrains/kotlin/fir/expressions/FirArgumentUtil.kt
index d08aeaba6a2..3792ed4d91a 100644
--- a/compiler/fir/tree/src/org/jetbrains/kotlin/fir/expressions/FirArgumentUtil.kt
+++ b/compiler/fir/tree/src/org/jetbrains/kotlin/fir/expressions/FirArgumentUtil.kt
@@ -5,12 +5,10 @@
 
 package org.jetbrains.kotlin.fir.expressions
 
-import org.jetbrains.kotlin.fir.FirElement
-import org.jetbrains.kotlin.fir.FirSourceElement
 import org.jetbrains.kotlin.fir.declarations.FirValueParameter
 import org.jetbrains.kotlin.fir.expressions.builder.buildArgumentList
-import org.jetbrains.kotlin.fir.visitors.FirTransformer
-import org.jetbrains.kotlin.fir.visitors.FirVisitor
+import org.jetbrains.kotlin.fir.expressions.impl.FirArraySetArgumentList
+import org.jetbrains.kotlin.fir.expressions.impl.FirResolvedArgumentList
 
 fun buildUnaryArgumentList(argument: FirExpression): FirArgumentList = buildArgumentList {
     arguments += argument
@@ -21,45 +19,13 @@ fun buildBinaryArgumentList(left: FirExpression, right: FirExpression): FirArgum
     arguments += right
 }
 
-abstract class FirAbstractArgumentList : FirArgumentList() {
-    override val source: FirSourceElement?
-        get() = null
+fun buildArraySetArgumentList(rValue: FirExpression, indexes: List<FirExpression>): FirArgumentList =
+    FirArraySetArgumentList(rValue, indexes)
 
-    override fun <D> transformArguments(transformer: FirTransformer<D>, data: D): FirArgumentList {
-        return this
-    }
-
-    override fun <R, D> acceptChildren(visitor: FirVisitor<R, D>, data: D) {
-        // DO NOTHING
-    }
-
-    override fun <D> transformChildren(transformer: FirTransformer<D>, data: D): FirElement {
-        return this
-    }
-}
+fun buildResolvedArgumentList(mapping: Map<FirExpression, FirValueParameter>): FirArgumentList =
+    FirResolvedArgumentList(mapping)
 
 object FirEmptyArgumentList : FirAbstractArgumentList() {
     override val arguments: List<FirExpression>
         get() = emptyList()
 }
-
-class FirArraySetArgumentList(
-    private val rValue: FirExpression,
-    private val indexes: List<FirExpression>
-) : FirAbstractArgumentList() {
-    override val arguments: List<FirExpression>
-        get() = indexes + rValue
-}
-
-class FirResolvedArgumentList(
-    val mapping: Map<FirExpression, FirValueParameter>
-) : FirAbstractArgumentList() {
-    override val arguments: List<FirExpression>
-        get() = mapping.keys.toList()
-
-    override fun <R, D> acceptChildren(visitor: FirVisitor<R, D>, data: D) {
-        for (argument in mapping.keys) {
-            argument.accept(visitor, data)
-        }
-    }
-}
\ No newline at end of file
diff --git a/compiler/fir/tree/src/org/jetbrains/kotlin/fir/expressions/impl/FirArraySetArgumentList.kt b/compiler/fir/tree/src/org/jetbrains/kotlin/fir/expressions/impl/FirArraySetArgumentList.kt
new file mode 100644
index 00000000000..ce2192eae14
--- /dev/null
+++ b/compiler/fir/tree/src/org/jetbrains/kotlin/fir/expressions/impl/FirArraySetArgumentList.kt
@@ -0,0 +1,17 @@
+/*
+ * Copyright 2010-2020 JetBrains s.r.o. and Kotlin Programming Language contributors.
+ * Use of this source code is governed by the Apache 2.0 license that can be found in the license/LICENSE.txt file.
+ */
+
+package org.jetbrains.kotlin.fir.expressions.impl
+
+import org.jetbrains.kotlin.fir.expressions.FirAbstractArgumentList
+import org.jetbrains.kotlin.fir.expressions.FirExpression
+
+class FirArraySetArgumentList internal constructor(
+    private val rValue: FirExpression,
+    private val indexes: List<FirExpression>
+) : FirAbstractArgumentList() {
+    override val arguments: List<FirExpression>
+        get() = indexes + rValue
+}
diff --git a/compiler/fir/tree/src/org/jetbrains/kotlin/fir/expressions/impl/FirResolvedArgumentList.kt b/compiler/fir/tree/src/org/jetbrains/kotlin/fir/expressions/impl/FirResolvedArgumentList.kt
new file mode 100644
index 00000000000..0d21296ce82
--- /dev/null
+++ b/compiler/fir/tree/src/org/jetbrains/kotlin/fir/expressions/impl/FirResolvedArgumentList.kt
@@ -0,0 +1,24 @@
+/*
+ * Copyright 2010-2020 JetBrains s.r.o. and Kotlin Programming Language contributors.
+ * Use of this source code is governed by the Apache 2.0 license that can be found in the license/LICENSE.txt file.
+ */
+
+package org.jetbrains.kotlin.fir.expressions.impl
+
+import org.jetbrains.kotlin.fir.declarations.FirValueParameter
+import org.jetbrains.kotlin.fir.expressions.FirAbstractArgumentList
+import org.jetbrains.kotlin.fir.expressions.FirExpression
+import org.jetbrains.kotlin.fir.visitors.FirVisitor
+
+class FirResolvedArgumentList internal constructor(
+    val mapping: Map<FirExpression, FirValueParameter>
+) : FirAbstractArgumentList() {
+    override val arguments: List<FirExpression>
+        get() = mapping.keys.toList()
+
+    override fun <R, D> acceptChildren(visitor: FirVisitor<R, D>, data: D) {
+        for (argument in mapping.keys) {
+            argument.accept(visitor, data)
+        }
+    }
+}