diff --git a/core/descriptor.loader.java/src/org/jetbrains/kotlin/load/java/lazy/descriptors/LazyJavaClassMemberScope.kt b/core/descriptor.loader.java/src/org/jetbrains/kotlin/load/java/lazy/descriptors/LazyJavaClassMemberScope.kt
index ebe8bbe62af..acdbabb9aff 100644
--- a/core/descriptor.loader.java/src/org/jetbrains/kotlin/load/java/lazy/descriptors/LazyJavaClassMemberScope.kt
+++ b/core/descriptor.loader.java/src/org/jetbrains/kotlin/load/java/lazy/descriptors/LazyJavaClassMemberScope.kt
@@ -70,7 +70,7 @@ class LazyJavaClassMemberScope(
     override fun computeMemberIndex(): MemberIndex {
         return object : ClassMemberIndex(jClass, { !it.isStatic }) {
             // For SAM-constructors
-            override fun getMethodNames(nameFilter: (Name) -> Boolean): Collection<Name>
+            override fun getMethodNames(nameFilter: (Name) -> Boolean): Set<Name>
                     = super.getMethodNames(nameFilter) + computeClassNames(DescriptorKindFilter.CLASSIFIERS, nameFilter)
         }
     }
@@ -660,10 +660,10 @@ class LazyJavaClassMemberScope(
         return super.getContributedVariables(name, location)
     }
 
-    override fun computeClassNames(kindFilter: DescriptorKindFilter, nameFilter: ((Name) -> Boolean)?): Collection<Name>
+    override fun computeClassNames(kindFilter: DescriptorKindFilter, nameFilter: ((Name) -> Boolean)?): Set<Name>
             = nestedClassIndex().keys + enumEntryIndex().keys
 
-    override fun computePropertyNames(kindFilter: DescriptorKindFilter, nameFilter: ((Name) -> Boolean)?): Collection<Name> {
+    override fun computePropertyNames(kindFilter: DescriptorKindFilter, nameFilter: ((Name) -> Boolean)?): Set<Name> {
         if (jClass.isAnnotationType) return memberIndex().getMethodNames(nameFilter ?: alwaysTrue())
 
         return memberIndex().getAllFieldNames() +
diff --git a/core/descriptor.loader.java/src/org/jetbrains/kotlin/load/java/lazy/descriptors/LazyJavaPackageScope.kt b/core/descriptor.loader.java/src/org/jetbrains/kotlin/load/java/lazy/descriptors/LazyJavaPackageScope.kt
index 5e12ef9bedb..8015cb7e49c 100644
--- a/core/descriptor.loader.java/src/org/jetbrains/kotlin/load/java/lazy/descriptors/LazyJavaPackageScope.kt
+++ b/core/descriptor.loader.java/src/org/jetbrains/kotlin/load/java/lazy/descriptors/LazyJavaPackageScope.kt
@@ -135,21 +135,21 @@ class LazyJavaPackageScope(
 
     override fun computeMemberIndex(): MemberIndex = object : MemberIndex by EMPTY_MEMBER_INDEX {
         // For SAM-constructors
-        override fun getMethodNames(nameFilter: (Name) -> Boolean): Collection<Name> = computeClassNames(DescriptorKindFilter.CLASSIFIERS, nameFilter)
+        override fun getMethodNames(nameFilter: (Name) -> Boolean): Set<Name> = computeClassNames(DescriptorKindFilter.CLASSIFIERS, nameFilter)
     }
 
-    override fun computeClassNames(kindFilter: DescriptorKindFilter, nameFilter: ((Name) -> Boolean)?): Collection<Name> {
+    override fun computeClassNames(kindFilter: DescriptorKindFilter, nameFilter: ((Name) -> Boolean)?): Set<Name> {
         // neither objects nor enum members can be in java package
-        if (!kindFilter.acceptsKinds(DescriptorKindFilter.NON_SINGLETON_CLASSIFIERS_MASK)) return listOf()
+        if (!kindFilter.acceptsKinds(DescriptorKindFilter.NON_SINGLETON_CLASSIFIERS_MASK)) return emptySet()
 
-        return jPackage.getClasses(nameFilter ?: alwaysTrue()).mapNotNull { klass ->
+        return jPackage.getClasses(nameFilter ?: alwaysTrue()).mapNotNullTo(linkedSetOf()) { klass ->
             if (klass.lightClassOriginKind == LightClassOriginKind.SOURCE) null else klass.name
         }
     }
 
-    override fun computeFunctionNames(kindFilter: DescriptorKindFilter, nameFilter: ((Name) -> Boolean)?): Collection<Name> {
+    override fun computeFunctionNames(kindFilter: DescriptorKindFilter, nameFilter: ((Name) -> Boolean)?): Set<Name> {
         // optimization: only SAM-constructors may exist in java package
-        if (kindFilter.excludes.contains(SamConstructorDescriptorKindExclude)) return listOf()
+        if (kindFilter.excludes.contains(SamConstructorDescriptorKindExclude)) return emptySet()
 
         return super.computeFunctionNames(kindFilter, nameFilter)
     }
@@ -160,7 +160,7 @@ class LazyJavaPackageScope(
         }?.let { result.add(it) }
     }
 
-    override fun computePropertyNames(kindFilter: DescriptorKindFilter, nameFilter: ((Name) -> Boolean)?) = listOf<Name>()
+    override fun computePropertyNames(kindFilter: DescriptorKindFilter, nameFilter: ((Name) -> Boolean)?) = emptySet<Name>()
 
     // we don't use implementation from super which caches all descriptors and does not use filters
     override fun getContributedDescriptors(kindFilter: DescriptorKindFilter, nameFilter: (Name) -> Boolean): Collection<DeclarationDescriptor> {
diff --git a/core/descriptor.loader.java/src/org/jetbrains/kotlin/load/java/lazy/descriptors/LazyJavaScope.kt b/core/descriptor.loader.java/src/org/jetbrains/kotlin/load/java/lazy/descriptors/LazyJavaScope.kt
index 7481f2ea7e7..89de53f2979 100644
--- a/core/descriptor.loader.java/src/org/jetbrains/kotlin/load/java/lazy/descriptors/LazyJavaScope.kt
+++ b/core/descriptor.loader.java/src/org/jetbrains/kotlin/load/java/lazy/descriptors/LazyJavaScope.kt
@@ -217,12 +217,12 @@ abstract class LazyJavaScope(protected val c: LazyJavaResolverContext) : MemberS
 
     override fun getContributedFunctions(name: Name, location: LookupLocation): Collection<SimpleFunctionDescriptor> = functions(name)
 
-    protected open fun computeFunctionNames(kindFilter: DescriptorKindFilter, nameFilter: ((Name) -> Boolean)?): Collection<Name>
+    protected open fun computeFunctionNames(kindFilter: DescriptorKindFilter, nameFilter: ((Name) -> Boolean)?): Set<Name>
             = memberIndex().getMethodNames(nameFilter ?: alwaysTrue())
 
     protected abstract fun computeNonDeclaredProperties(name: Name, result: MutableCollection<PropertyDescriptor>)
 
-    protected abstract fun computePropertyNames(kindFilter: DescriptorKindFilter, nameFilter: ((Name) -> Boolean)?): Collection<Name>
+    protected abstract fun computePropertyNames(kindFilter: DescriptorKindFilter, nameFilter: ((Name) -> Boolean)?): Set<Name>
 
     private val properties = c.storageManager.createMemoizedFunction {
         name: Name ->
@@ -328,7 +328,7 @@ abstract class LazyJavaScope(protected val c: LazyJavaResolverContext) : MemberS
         return result.toReadOnlyList()
     }
 
-    protected abstract fun computeClassNames(kindFilter: DescriptorKindFilter, nameFilter: ((Name) -> Boolean)?): Collection<Name>
+    protected abstract fun computeClassNames(kindFilter: DescriptorKindFilter, nameFilter: ((Name) -> Boolean)?): Set<Name>
 
     override fun toString() = "Lazy scope for $ownerDescriptor"
 
diff --git a/core/descriptor.loader.java/src/org/jetbrains/kotlin/load/java/lazy/descriptors/LazyJavaStaticClassScope.kt b/core/descriptor.loader.java/src/org/jetbrains/kotlin/load/java/lazy/descriptors/LazyJavaStaticClassScope.kt
index 150969c8265..ed561736b95 100644
--- a/core/descriptor.loader.java/src/org/jetbrains/kotlin/load/java/lazy/descriptors/LazyJavaStaticClassScope.kt
+++ b/core/descriptor.loader.java/src/org/jetbrains/kotlin/load/java/lazy/descriptors/LazyJavaStaticClassScope.kt
@@ -42,7 +42,7 @@ class LazyJavaStaticClassScope(
     override fun computeMemberIndex(): MemberIndex {
         val delegate = ClassMemberIndex(jClass) { it.isStatic }
         return object : MemberIndex by delegate {
-            override fun getMethodNames(nameFilter: (Name) -> Boolean): Collection<Name> {
+            override fun getMethodNames(nameFilter: (Name) -> Boolean): Set<Name> {
                 // Should be a super call, but KT-2860
                 return delegate.getMethodNames(nameFilter) +
                        // For SAM-constructors
@@ -51,17 +51,17 @@ class LazyJavaStaticClassScope(
         }
     }
 
-    override fun computeFunctionNames(kindFilter: DescriptorKindFilter, nameFilter: ((Name) -> Boolean)?): Collection<Name> {
+    override fun computeFunctionNames(kindFilter: DescriptorKindFilter, nameFilter: ((Name) -> Boolean)?): Set<Name> {
         if (jClass.isEnum) {
             return super.computeFunctionNames(kindFilter, nameFilter) + listOf(DescriptorUtils.ENUM_VALUE_OF, DescriptorUtils.ENUM_VALUES)
         }
         return super.computeFunctionNames(kindFilter, nameFilter)
     }
 
-    override fun computePropertyNames(kindFilter: DescriptorKindFilter, nameFilter: ((Name) -> Boolean)?): Collection<Name> =
+    override fun computePropertyNames(kindFilter: DescriptorKindFilter, nameFilter: ((Name) -> Boolean)?): Set<Name> =
             memberIndex().getAllFieldNames()
 
-    override fun computeClassNames(kindFilter: DescriptorKindFilter, nameFilter: ((Name) -> Boolean)?): Collection<Name> = listOf()
+    override fun computeClassNames(kindFilter: DescriptorKindFilter, nameFilter: ((Name) -> Boolean)?): Set<Name> = emptySet()
 
     override fun getContributedClassifier(name: Name, location: LookupLocation): ClassifierDescriptor? {
         // We don't need to track lookups here because we find nested/inner classes in LazyJavaClassMemberScope
diff --git a/core/descriptor.loader.java/src/org/jetbrains/kotlin/load/java/lazy/descriptors/MemberIndex.kt b/core/descriptor.loader.java/src/org/jetbrains/kotlin/load/java/lazy/descriptors/MemberIndex.kt
index 0e7a33b2649..ee87924e619 100644
--- a/core/descriptor.loader.java/src/org/jetbrains/kotlin/load/java/lazy/descriptors/MemberIndex.kt
+++ b/core/descriptor.loader.java/src/org/jetbrains/kotlin/load/java/lazy/descriptors/MemberIndex.kt
@@ -27,18 +27,18 @@ import java.util.*
 
 interface MemberIndex {
     fun findMethodsByName(name: Name): Collection<JavaMethod>
-    fun getMethodNames(nameFilter: (Name) -> Boolean): Collection<Name>
+    fun getMethodNames(nameFilter: (Name) -> Boolean): Set<Name>
 
     fun findFieldByName(name: Name): JavaField?
-    fun getAllFieldNames(): Collection<Name>
+    fun getAllFieldNames(): Set<Name>
 }
 
 object EMPTY_MEMBER_INDEX : MemberIndex {
     override fun findMethodsByName(name: Name) = listOf<JavaMethod>()
-    override fun getMethodNames(nameFilter: (Name) -> Boolean) = listOf<Name>()
+    override fun getMethodNames(nameFilter: (Name) -> Boolean) = emptySet<Name>()
 
     override fun findFieldByName(name: Name): JavaField? = null
-    override fun getAllFieldNames() = listOf<Name>()
+    override fun getAllFieldNames() = emptySet<Name>()
 }
 
 private val ADDITIONAL_MEMBER_NAMES_MAP = mapOf(
@@ -61,11 +61,11 @@ open class ClassMemberIndex(val jClass: JavaClass, val memberFilter: (JavaMember
     private val fields = jClass.fields.asSequence().filter(memberFilter).associateBy { m -> m.name }
 
     override fun findMethodsByName(name: Name): Collection<JavaMethod> = methods[name] ?: listOf()
-    override fun getMethodNames(nameFilter: (Name) -> Boolean): Collection<Name> =
+    override fun getMethodNames(nameFilter: (Name) -> Boolean): Set<Name> =
             jClass.getAllMemberNames(methodFilter) { methods }
 
     override fun findFieldByName(name: Name): JavaField? = fields[name]
-    override fun getAllFieldNames(): Collection<Name> = jClass.getAllMemberNames(memberFilter) { fields }
+    override fun getAllFieldNames(): Set<Name> = jClass.getAllMemberNames(memberFilter) { fields }
 }
 
 private fun JavaClass.getNonDeclaredMethodNames(): List<Name> {