diff --git a/backend.native/compiler/ir/backend.native/src/org/jetbrains/kotlin/backend/konan/KonanLower.kt b/backend.native/compiler/ir/backend.native/src/org/jetbrains/kotlin/backend/konan/KonanLower.kt
index 602d02b8caa..8ecf67293a6 100644
--- a/backend.native/compiler/ir/backend.native/src/org/jetbrains/kotlin/backend/konan/KonanLower.kt
+++ b/backend.native/compiler/ir/backend.native/src/org/jetbrains/kotlin/backend/konan/KonanLower.kt
@@ -17,6 +17,10 @@ internal class KonanLower(val context: Context) {
     fun lower(irFile: IrFile) {
         val phaser = PhaseManager(context)
 
+        // TODO: consider place of the pass.
+        phaser.phase(KonanPhase.LOWER_STRING_CONCAT) {
+            StringConcatenationLowering(context).lower(irFile)
+        }
         phaser.phase(KonanPhase.LOWER_INLINE) {
             //FunctionInlining(context).inline(irFile)
         }
diff --git a/backend.native/compiler/ir/backend.native/src/org/jetbrains/kotlin/backend/konan/KonanPhases.kt b/backend.native/compiler/ir/backend.native/src/org/jetbrains/kotlin/backend/konan/KonanPhases.kt
index 8ab4548e3b7..116afa093c1 100644
--- a/backend.native/compiler/ir/backend.native/src/org/jetbrains/kotlin/backend/konan/KonanPhases.kt
+++ b/backend.native/compiler/ir/backend.native/src/org/jetbrains/kotlin/backend/konan/KonanPhases.kt
@@ -22,6 +22,7 @@ enum class KonanPhase(val description: String,
     /* ... ... */ AUTOBOX("Autoboxing of primitive types"),
     /* ... ... */ LOWER_ENUMS("Enum classes lowering"),
     /* ... ... */ LOWER_INNER_CLASSES("Inner classes lowering"),
+    /* ... ... */ LOWER_STRING_CONCAT("String concatenation lowering"),
     /* ... */ BITCODE("LLVM BitCode Generation"),
     /* ... ... */ RTTI("RTTI Generation"),
     /* ... ... */ CODEGEN("Code Generation"),
diff --git a/backend.native/compiler/ir/backend.native/src/org/jetbrains/kotlin/backend/konan/KonanPlatform.kt b/backend.native/compiler/ir/backend.native/src/org/jetbrains/kotlin/backend/konan/KonanPlatform.kt
index f0ced1ebbab..6b86820abaf 100644
--- a/backend.native/compiler/ir/backend.native/src/org/jetbrains/kotlin/backend/konan/KonanPlatform.kt
+++ b/backend.native/compiler/ir/backend.native/src/org/jetbrains/kotlin/backend/konan/KonanPlatform.kt
@@ -18,6 +18,7 @@ package org.jetbrains.kotlin.backend.konan
 
 import org.jetbrains.kotlin.builtins.KotlinBuiltIns
 import org.jetbrains.kotlin.backend.konan.KonanPlatformConfigurator
+import org.jetbrains.kotlin.builtins.PrimitiveType
 import org.jetbrains.kotlin.resolve.ImportPath
 import org.jetbrains.kotlin.resolve.MultiTargetPlatform
 import org.jetbrains.kotlin.resolve.PlatformConfigurator
@@ -31,7 +32,6 @@ class KonanBuiltIns: KotlinBuiltIns {
     constructor(storageManager: StorageManager, withModule: Boolean) : this(storageManager) {
         if (withModule) createBuiltInsModule()
     }
-
 }
 
 object KonanPlatform : TargetPlatform("Konan") {
diff --git a/backend.native/compiler/ir/backend.native/src/org/jetbrains/kotlin/backend/konan/ir/IrBuilders.kt b/backend.native/compiler/ir/backend.native/src/org/jetbrains/kotlin/backend/konan/ir/IrBuilders.kt
index a1ace20a169..1c3ed8593be 100644
--- a/backend.native/compiler/ir/backend.native/src/org/jetbrains/kotlin/backend/konan/ir/IrBuilders.kt
+++ b/backend.native/compiler/ir/backend.native/src/org/jetbrains/kotlin/backend/konan/ir/IrBuilders.kt
@@ -3,12 +3,18 @@ package org.jetbrains.kotlin.backend.konan.ir
 import org.jetbrains.kotlin.descriptors.VariableDescriptor
 import org.jetbrains.kotlin.ir.builders.*
 import org.jetbrains.kotlin.ir.expressions.IrExpression
+import org.jetbrains.kotlin.ir.expressions.IrStatementOrigin
+import org.jetbrains.kotlin.types.KotlinType
 
-inline fun IrBlockBuilder.irLetSequence(
+inline fun IrBuilderWithScope.irLetSequence(
         value: IrExpression,
         nameHint: String? = null,
+        startOffset: Int = this.startOffset,
+        endOffset: Int = this.endOffset,
+        origin: IrStatementOrigin? = null,
+        resultType: KotlinType? = null,
         body: IrBlockBuilder.(VariableDescriptor) -> Unit
-): IrExpression  = block {
+): IrExpression  = irBlock(startOffset, endOffset, origin, resultType) {
     val irTemporary = defineTemporary(value, nameHint)
     this.body(irTemporary)
-}
+}
\ No newline at end of file
diff --git a/backend.native/compiler/ir/backend.native/src/org/jetbrains/kotlin/backend/konan/lower/StringConcatenationLowering.kt b/backend.native/compiler/ir/backend.native/src/org/jetbrains/kotlin/backend/konan/lower/StringConcatenationLowering.kt
new file mode 100644
index 00000000000..8ee8ae7545b
--- /dev/null
+++ b/backend.native/compiler/ir/backend.native/src/org/jetbrains/kotlin/backend/konan/lower/StringConcatenationLowering.kt
@@ -0,0 +1,102 @@
+package org.jetbrains.kotlin.backend.konan.lower
+
+import org.jetbrains.kotlin.backend.common.FileLoweringPass
+import org.jetbrains.kotlin.backend.konan.Context
+import org.jetbrains.kotlin.backend.konan.descriptors.signature2Descriptor
+import org.jetbrains.kotlin.backend.konan.ir.irLetSequence
+import org.jetbrains.kotlin.builtins.PrimitiveType
+import org.jetbrains.kotlin.descriptors.CallableDescriptor
+import org.jetbrains.kotlin.descriptors.ClassDescriptor
+import org.jetbrains.kotlin.incremental.components.NoLookupLocation
+import org.jetbrains.kotlin.ir.IrStatement
+import org.jetbrains.kotlin.ir.builders.*
+import org.jetbrains.kotlin.ir.declarations.IrDeclaration
+import org.jetbrains.kotlin.ir.declarations.IrFile
+import org.jetbrains.kotlin.ir.expressions.IrExpression
+import org.jetbrains.kotlin.ir.expressions.IrStringConcatenation
+import org.jetbrains.kotlin.ir.visitors.IrElementTransformerVoid
+import org.jetbrains.kotlin.ir.visitors.transformChildrenVoid
+import org.jetbrains.kotlin.name.FqName
+import org.jetbrains.kotlin.name.Name
+import org.jetbrains.kotlin.types.KotlinType
+
+
+/**
+ * This lowering pass replaces [IrStringConcatenation]s with StringBuilder appends.
+ */
+internal class StringConcatenationLowering(val context: Context) : FileLoweringPass {
+    override fun lower(irFile: IrFile) {
+        irFile.transformChildrenVoid(StringConcatenationTransformer(this))
+    }
+}
+
+private class StringConcatenationTransformer(val lower: StringConcatenationLowering) : IrElementTransformerVoid() {
+
+    private val buildersStack = mutableListOf<IrBuilderWithScope>()
+    private val context = lower.context
+    private val builtIns = context.builtIns
+
+    private val typesWithSpecialAppendFunction =
+            PrimitiveType.values().map { builtIns.getPrimitiveKotlinType(it) } + builtIns.stringType
+
+    private val kotlinTextFqName = FqName.fromSegments(listOf("kotlin", "text"))
+    private val nameToString = Name.identifier("toString")
+    private val nameStringBuilder = Name.identifier("StringBuilder")
+    private val nameAppend = Name.identifier("append")
+
+    private val classStringBuilder = builtIns.builtInsModule.getPackage(kotlinTextFqName).
+            memberScope.getContributedClassifier(nameStringBuilder,
+            NoLookupLocation.FROM_BACKEND) as ClassDescriptor
+
+    //TODO: calculate and pass string length to the constructor.
+    private val constructor = classStringBuilder.constructors.firstOrNull {
+        it.valueParameters.size == 0
+    }!!
+
+    private val toStringFunction = classStringBuilder.signature2Descriptor(nameToString)!!
+    private val defaultAppendFunction =
+            classStringBuilder.signature2Descriptor(nameAppend, arrayOf(builtIns.nullableAnyType))!!
+
+    private val appendFunctions: Map<KotlinType, CallableDescriptor?> =
+            typesWithSpecialAppendFunction.map {
+                it to classStringBuilder.signature2Descriptor(nameAppend, arrayOf(it))
+            }.toMap()
+
+    private fun typeToAppendFunction(type : KotlinType) : CallableDescriptor {
+        return appendFunctions[type]?:defaultAppendFunction
+    }
+
+    override fun visitStringConcatenation(expression: IrStringConcatenation): IrExpression {
+        assert(!buildersStack.isEmpty())
+
+        val blockBuilder = buildersStack.last()
+
+        return blockBuilder.irLetSequence(
+                value = blockBuilder.irCall(constructor),
+                startOffset = expression.startOffset,
+                endOffset = expression.endOffset,
+                resultType = expression.type) { stringBuilderImpl ->
+            expression.arguments.forEach { arg ->
+                val appendFunction = typeToAppendFunction(arg.type)
+                +irCall(appendFunction).apply {
+                    dispatchReceiver = irGet(stringBuilderImpl)
+                    putValueArgument(0, arg)
+                }
+            }
+            +irCall(toStringFunction).apply {
+                dispatchReceiver = irGet(stringBuilderImpl)
+            }
+        }
+    }
+
+    override fun visitDeclaration(declaration: IrDeclaration): IrStatement {
+        with(declaration) {
+            buildersStack.add(
+                    IrBlockBuilder(IrGeneratorContext(context.irBuiltIns), Scope(descriptor), startOffset, endOffset)
+            )
+            transformChildrenVoid(this@StringConcatenationTransformer)
+            buildersStack.removeAt(buildersStack.lastIndex)
+            return this@with
+        }
+    }
+}
\ No newline at end of file