diff --git a/core/descriptors/src/org/jetbrains/jet/lang/types/flexibleTypes.kt b/core/descriptors/src/org/jetbrains/jet/lang/types/flexibleTypes.kt
index 5921328bcb8..0b76e32371d 100644
--- a/core/descriptors/src/org/jetbrains/jet/lang/types/flexibleTypes.kt
+++ b/core/descriptors/src/org/jetbrains/jet/lang/types/flexibleTypes.kt
@@ -61,6 +61,11 @@ public trait Flexibility : TypeCapability, SubtypingRepresentatives {
 public fun JetType.isFlexible(): Boolean = this.getCapability(javaClass<Flexibility>()) != null
 public fun JetType.flexibility(): Flexibility = this.getCapability(javaClass<Flexibility>())!!
 
+public fun JetType.isNullabilityFlexible(): Boolean {
+    val flexibility = this.getCapability(javaClass<Flexibility>()) ?: return false
+    return TypeUtils.isNullableType(flexibility.lowerBound) != TypeUtils.isNullableType(flexibility.upperBound)
+}
+
 // This function is intended primarily for sets: since JetType.equals() represents _syntactical_ equality of types,
 // whereas JetTypeChecker.DEFAULT.equalsTypes() represents semantical equality
 // A set of types (e.g. exact bounds etc) may contain, for example, X, X? and X!
diff --git a/idea/ide-common/src/org/jetbrains/jet/plugin/util/FuzzyType.kt b/idea/ide-common/src/org/jetbrains/jet/plugin/util/FuzzyType.kt
index 9cbdc5e9175..c779aee83d2 100644
--- a/idea/ide-common/src/org/jetbrains/jet/plugin/util/FuzzyType.kt
+++ b/idea/ide-common/src/org/jetbrains/jet/plugin/util/FuzzyType.kt
@@ -42,7 +42,7 @@ fun CallableDescriptor.fuzzyExtensionReceiverType(): FuzzyType? {
 
 fun FuzzyType.makeNotNullable() = FuzzyType(type.makeNotNullable(), freeParameters)
 fun FuzzyType.makeNullable() = FuzzyType(type.makeNullable(), freeParameters)
-fun FuzzyType.isNullable() = type.isMarkedNullable()
+fun FuzzyType.nullability() = type.nullability()
 
 class FuzzyType(
         val type: JetType,
diff --git a/idea/ide-common/src/org/jetbrains/jet/plugin/util/TypeUtils.kt b/idea/ide-common/src/org/jetbrains/jet/plugin/util/TypeUtils.kt
index c6c45c4a8e0..e9065334bbe 100644
--- a/idea/ide-common/src/org/jetbrains/jet/plugin/util/TypeUtils.kt
+++ b/idea/ide-common/src/org/jetbrains/jet/plugin/util/TypeUtils.kt
@@ -29,6 +29,7 @@ import org.jetbrains.jet.lang.types.isFlexible
 import org.jetbrains.jet.lang.types.flexibility
 import java.util.LinkedHashSet
 import org.jetbrains.jet.lang.types.isDynamic
+import org.jetbrains.jet.lang.types.isNullabilityFlexible
 
 fun JetType.makeNullable() = TypeUtils.makeNullable(this)
 fun JetType.makeNotNullable() = TypeUtils.makeNotNullable(this)
@@ -78,4 +79,18 @@ public fun JetType.getAllReferencedTypes(): Set<JetType> {
 
     addType(this)
     return types
+}
+
+public enum class TypeNullability {
+    NOT_NULL
+    NULLABLE
+    FLEXIBLE
+}
+
+public fun JetType.nullability(): TypeNullability {
+    return when {
+        isNullabilityFlexible() -> TypeNullability.FLEXIBLE
+        TypeUtils.isNullableType(this) -> TypeNullability.NULLABLE
+        else -> TypeNullability.NOT_NULL
+    }
 }
\ No newline at end of file
diff --git a/idea/ide-common/src/org/jetbrains/jet/plugin/util/extensionsUtils.kt b/idea/ide-common/src/org/jetbrains/jet/plugin/util/extensionsUtils.kt
index f816f3e0160..32390ebe48e 100644
--- a/idea/ide-common/src/org/jetbrains/jet/plugin/util/extensionsUtils.kt
+++ b/idea/ide-common/src/org/jetbrains/jet/plugin/util/extensionsUtils.kt
@@ -23,7 +23,6 @@ import org.jetbrains.jet.lang.resolve.calls.smartcasts.DataFlowInfo
 import org.jetbrains.jet.lang.resolve.scopes.JetScope
 import org.jetbrains.jet.lang.descriptors.SimpleFunctionDescriptor
 import org.jetbrains.jet.lang.resolve.calls.smartcasts.SmartCastUtils
-import org.jetbrains.jet.lang.types.TypeUtils
 import org.jetbrains.jet.lang.descriptors.DeclarationDescriptor
 
 public enum class CallType {
@@ -79,7 +78,7 @@ public fun CallableDescriptor.substituteExtensionIfCallable(
             .map {
                 var substitutor = extensionReceiverType.checkIsSuperTypeOf(it)
                 // check if we may fail due to receiver expression being nullable
-                if (substitutor == null && TypeUtils.isNullableType(it) && !TypeUtils.isNullableType(extensionReceiverType.type)) {
+                if (substitutor == null && it.nullability() == TypeNullability.NULLABLE && extensionReceiverType.nullability() == TypeNullability.NOT_NULL) {
                     substitutor = extensionReceiverType.checkIsSuperTypeOf(it.makeNotNullable())
                 }
                 substitutor
diff --git a/idea/src/org/jetbrains/jet/plugin/completion/LookupElementFactory.kt b/idea/src/org/jetbrains/jet/plugin/completion/LookupElementFactory.kt
index ee7ad00b6a4..b8209b2e580 100644
--- a/idea/src/org/jetbrains/jet/plugin/completion/LookupElementFactory.kt
+++ b/idea/src/org/jetbrains/jet/plugin/completion/LookupElementFactory.kt
@@ -38,6 +38,8 @@ import org.jetbrains.jet.plugin.caches.resolve.ResolutionFacade
 import com.intellij.codeInsight.lookup.DefaultLookupItemRenderer
 import org.jetbrains.jet.lang.types.TypeUtils
 import com.intellij.codeInsight.lookup.impl.LookupCellRenderer
+import org.jetbrains.jet.plugin.util.nullability
+import org.jetbrains.jet.plugin.util.TypeNullability
 
 public class LookupElementFactory(
         private val receiverTypes: Collection<JetType>
@@ -207,12 +209,12 @@ public class LookupElementFactory(
     private fun callableWeight(descriptor: DeclarationDescriptor): CallableWeight? {
         if (descriptor !is CallableDescriptor) return null
 
-        val isReceiverNullable = receiverTypes.isNotEmpty() && receiverTypes.all { it.isMarkedNullable() }
+        val isReceiverNullable = receiverTypes.isNotEmpty() && receiverTypes.all { it.nullability() == TypeNullability.NULLABLE }
         val receiverParameter = descriptor.getExtensionReceiverParameter()
 
         if (receiverParameter != null) {
             val receiverParamType = receiverParameter.getType()
-            return if (isReceiverNullable && !receiverParamType.isMarkedNullable())
+            return if (isReceiverNullable && receiverParamType.nullability() == TypeNullability.NOT_NULL)
                 CallableWeight.notApplicableReceiverNullable
             else if (receiverTypes.any { TypeUtils.equalTypes(it, receiverParamType) })
                 CallableWeight.thisTypeExtension
diff --git a/idea/src/org/jetbrains/jet/plugin/completion/smart/Utils.kt b/idea/src/org/jetbrains/jet/plugin/completion/smart/Utils.kt
index e6d6b49e48e..06367592d6a 100644
--- a/idea/src/org/jetbrains/jet/plugin/completion/smart/Utils.kt
+++ b/idea/src/org/jetbrains/jet/plugin/completion/smart/Utils.kt
@@ -41,8 +41,9 @@ import org.jetbrains.jet.lang.types.TypeSubstitutor
 import java.util.ArrayList
 import java.util.HashMap
 import org.jetbrains.jet.plugin.util.FuzzyType
-import org.jetbrains.jet.plugin.util.isNullable
 import org.jetbrains.jet.plugin.util.makeNotNullable
+import org.jetbrains.jet.plugin.util.nullability
+import org.jetbrains.jet.plugin.util.TypeNullability
 
 class ArtificialElementInsertHandler(
         val textBeforeCaret: String, val textAfterCaret: String, val shortenRefs: Boolean) : InsertHandler<LookupElement>{
@@ -117,7 +118,7 @@ fun Collection<FuzzyType>.classifyExpectedInfo(expectedInfo: ExpectedInfo): Expe
         return ExpectedInfoClassification.matches(substitutor)
     }
 
-    if (stream.any { it.isNullable() }) {
+    if (stream.any { it.nullability() == TypeNullability.NULLABLE }) {
         val substitutor2 = stream.map { it.makeNotNullable().checkIsSubtypeOf(expectedInfo.type) }.firstOrNull()
         if (substitutor2 != null) {
             return ExpectedInfoClassification.matchesIfNotNullable(substitutor2)