diff --git a/compiler/resolution/src/org/jetbrains/kotlin/resolve/calls/tower/TowerResolver.kt b/compiler/resolution/src/org/jetbrains/kotlin/resolve/calls/tower/TowerResolver.kt
index e19b85ae573..c584ce8316e 100644
--- a/compiler/resolution/src/org/jetbrains/kotlin/resolve/calls/tower/TowerResolver.kt
+++ b/compiler/resolution/src/org/jetbrains/kotlin/resolve/calls/tower/TowerResolver.kt
@@ -270,7 +270,7 @@ class TowerResolver {
         val candidatesGroups = if (useOrder) {
             processor.process(towerData)
         } else {
-            listOf(processor.process(towerData).flatMap { it })
+            listOf(processor.process(towerData).flatten())
         }
 
         for (candidatesGroup in candidatesGroups) {
diff --git a/idea/ide-common/src/org/jetbrains/kotlin/resolve/lazy/PartialBodyResolveFilter.kt b/idea/ide-common/src/org/jetbrains/kotlin/resolve/lazy/PartialBodyResolveFilter.kt
index 99db8d0ba54..ea6cf202d19 100644
--- a/idea/ide-common/src/org/jetbrains/kotlin/resolve/lazy/PartialBodyResolveFilter.kt
+++ b/idea/ide-common/src/org/jetbrains/kotlin/resolve/lazy/PartialBodyResolveFilter.kt
@@ -116,7 +116,7 @@ class PartialBodyResolveFilter(
                 if (!smartCastPlaces.isEmpty()) {
                     //TODO: do we really need correct resolve for ALL smart cast places?
                     smartCastPlaces.values
-                            .flatMap { it }
+                            .flatten()
                             .forEach { statementMarks.mark(it, MarkLevel.NEED_REFERENCE_RESOLVE) }
                     updateNameFilter()
                 }
diff --git a/idea/idea-analysis/src/org/jetbrains/kotlin/idea/search/usagesSearch/ExpressionsOfTypeProcessor.kt b/idea/idea-analysis/src/org/jetbrains/kotlin/idea/search/usagesSearch/ExpressionsOfTypeProcessor.kt
index 365e86f41a5..1bd390c05f6 100644
--- a/idea/idea-analysis/src/org/jetbrains/kotlin/idea/search/usagesSearch/ExpressionsOfTypeProcessor.kt
+++ b/idea/idea-analysis/src/org/jetbrains/kotlin/idea/search/usagesSearch/ExpressionsOfTypeProcessor.kt
@@ -149,7 +149,7 @@ class ExpressionsOfTypeProcessor(
 
         runReadAction {
             val scopeElements = scopesToUsePlainSearch.values
-                    .flatMap { it }
+                    .flatten()
                     .filter { it.isValid }
                     .toTypedArray()
             if (scopeElements.isNotEmpty()) {
diff --git a/idea/src/org/jetbrains/kotlin/idea/codeInsight/KotlinCopyPasteReferenceProcessor.kt b/idea/src/org/jetbrains/kotlin/idea/codeInsight/KotlinCopyPasteReferenceProcessor.kt
index bc2500f9e4d..8e3c8d390eb 100644
--- a/idea/src/org/jetbrains/kotlin/idea/codeInsight/KotlinCopyPasteReferenceProcessor.kt
+++ b/idea/src/org/jetbrains/kotlin/idea/codeInsight/KotlinCopyPasteReferenceProcessor.kt
@@ -128,7 +128,7 @@ class KotlinCopyPasteReferenceProcessor : CopyPastePostProcessor<KotlinReference
             file.elementsInRange(it).filter { it is KtElement || it is KDocElement }
         })
 
-        val allElementsToResolve = elementsByRange.values.flatMap { it }.flatMap { it.collectDescendantsOfType<KtElement>() }
+        val allElementsToResolve = elementsByRange.values.flatten().flatMap { it.collectDescendantsOfType<KtElement>() }
         val bindingContext = file.getResolutionFacade().analyze(allElementsToResolve, BodyResolveMode.PARTIAL)
 
         val result = ArrayList<KotlinReferenceData>()
diff --git a/j2k/src/org/jetbrains/kotlin/j2k/JavaToKotlinConverter.kt b/j2k/src/org/jetbrains/kotlin/j2k/JavaToKotlinConverter.kt
index 71a4ee297df..7a7921134a3 100644
--- a/j2k/src/org/jetbrains/kotlin/j2k/JavaToKotlinConverter.kt
+++ b/j2k/src/org/jetbrains/kotlin/j2k/JavaToKotlinConverter.kt
@@ -157,7 +157,7 @@ class JavaToKotlinConverter(
         if (usageProcessings.isEmpty()) return null
 
         val map: Map<PsiElement, Collection<UsageProcessing>> = usageProcessings.values
-                .flatMap { it }
+                .flatten()
                 .filter { it.javaCodeProcessors.isNotEmpty() || it.kotlinCodeProcessors.isNotEmpty() }
                 .groupBy { it.targetElement }
         if (map.isEmpty()) return null