diff --git a/compiler/frontend.java/src/org/jetbrains/kotlin/load/java/sam/SamConversionResolverImpl.kt b/compiler/frontend.java/src/org/jetbrains/kotlin/load/java/sam/SamConversionResolverImpl.kt
index fccd048386f..e7ee9d71672 100644
--- a/compiler/frontend.java/src/org/jetbrains/kotlin/load/java/sam/SamConversionResolverImpl.kt
+++ b/compiler/frontend.java/src/org/jetbrains/kotlin/load/java/sam/SamConversionResolverImpl.kt
@@ -25,7 +25,7 @@ import org.jetbrains.kotlin.load.java.descriptors.JavaConstructorDescriptor
 import org.jetbrains.kotlin.load.java.descriptors.JavaMethodDescriptor
 import org.jetbrains.kotlin.load.java.descriptors.SamConstructorDescriptor
 import org.jetbrains.kotlin.load.java.lazy.descriptors.LazyJavaClassDescriptor
-import org.jetbrains.kotlin.types.KotlinType
+import org.jetbrains.kotlin.types.SimpleType
 
 object SamConversionResolverImpl : SamConversionResolver {
     override fun resolveSamConstructor(constructorOwner: DeclarationDescriptor, classifier: () -> ClassifierDescriptor?): SamConstructorDescriptor? {
@@ -44,7 +44,7 @@ object SamConversionResolverImpl : SamConversionResolver {
         }
     }
 
-    override fun resolveFunctionTypeIfSamInterface(classDescriptor: JavaClassDescriptor): KotlinType? {
+    override fun resolveFunctionTypeIfSamInterface(classDescriptor: JavaClassDescriptor): SimpleType? {
         val abstractMethod = SingleAbstractMethodUtils.getSingleAbstractMethodOrNull(classDescriptor) ?: return null
         return SingleAbstractMethodUtils.getFunctionTypeForAbstractMethod(abstractMethod)
     }
diff --git a/compiler/frontend.java/src/org/jetbrains/kotlin/load/java/sam/SingleAbstractMethodUtils.java b/compiler/frontend.java/src/org/jetbrains/kotlin/load/java/sam/SingleAbstractMethodUtils.java
index b422f71e4ea..e6999c57cb6 100644
--- a/compiler/frontend.java/src/org/jetbrains/kotlin/load/java/sam/SingleAbstractMethodUtils.java
+++ b/compiler/frontend.java/src/org/jetbrains/kotlin/load/java/sam/SingleAbstractMethodUtils.java
@@ -23,7 +23,6 @@ import org.jetbrains.kotlin.descriptors.annotations.Annotations;
 import org.jetbrains.kotlin.descriptors.impl.TypeParameterDescriptorImpl;
 import org.jetbrains.kotlin.descriptors.impl.ValueParameterDescriptorImpl;
 import org.jetbrains.kotlin.load.java.descriptors.*;
-import org.jetbrains.kotlin.load.java.lazy.types.LazyJavaTypeResolver;
 import org.jetbrains.kotlin.name.Name;
 import org.jetbrains.kotlin.resolve.DescriptorUtils;
 import org.jetbrains.kotlin.resolve.FunctionTypeResolveUtilsKt;
@@ -55,15 +54,31 @@ public class SingleAbstractMethodUtils {
 
     @Nullable
     public static KotlinType getFunctionTypeForSamType(@NotNull KotlinType samType) {
+        UnwrappedType unwrappedType = samType.unwrap();
+        if (unwrappedType instanceof FlexibleType) {
+            SimpleType lower = getFunctionTypeForSamType(((FlexibleType) unwrappedType).getLowerBound());
+            SimpleType upper = getFunctionTypeForSamType(((FlexibleType) unwrappedType).getUpperBound());
+            assert (lower == null) == (upper == null) : "Illegal flexible type: " + unwrappedType;
+
+            if (upper == null) return null;
+            return KotlinTypeFactory.flexibleType(lower, upper);
+        }
+        else {
+            return getFunctionTypeForSamType((SimpleType) unwrappedType);
+        }
+    }
+
+    @Nullable
+    private static SimpleType getFunctionTypeForSamType(@NotNull SimpleType samType) {
         // e.g. samType == Comparator<String>?
 
         ClassifierDescriptor classifier = samType.getConstructor().getDeclarationDescriptor();
         if (classifier instanceof JavaClassDescriptor) {
             // Function2<T, T, Int>
-            KotlinType functionTypeDefault = ((JavaClassDescriptor) classifier).getFunctionTypeForSamInterface();
+            SimpleType functionTypeDefault = ((JavaClassDescriptor) classifier).getFunctionTypeForSamInterface();
 
             if (functionTypeDefault != null) {
-                KotlinType noProjectionsSamType = SingleAbstractMethodUtilsKt.nonProjectionParametrization(samType);
+                SimpleType noProjectionsSamType = SingleAbstractMethodUtilsKt.nonProjectionParametrization(samType);
                 if (noProjectionsSamType == null) return null;
 
                 // Function2<String, String, Int>?
@@ -71,19 +86,16 @@ public class SingleAbstractMethodUtils {
                 assert type != null : "Substitution based on type with no projections '" + noProjectionsSamType +
                                       "' should not end with conflict";
 
-                if (FlexibleTypesKt.isNullabilityFlexible(samType)) {
-                    SimpleType simpleType = KotlinTypeKt.asSimpleType(type);
-                    return KotlinTypeFactory.flexibleType(simpleType, simpleType.makeNullableAsSpecified(true));
-                }
+                SimpleType simpleType = KotlinTypeKt.asSimpleType(type);
 
-                return TypeUtils.makeNullableAsSpecified(type, samType.isMarkedNullable());
+                return simpleType.makeNullableAsSpecified(samType.isMarkedNullable());
             }
         }
         return null;
     }
 
     @NotNull
-    public static KotlinType getFunctionTypeForAbstractMethod(@NotNull FunctionDescriptor function) {
+    public static SimpleType getFunctionTypeForAbstractMethod(@NotNull FunctionDescriptor function) {
         KotlinType returnType = function.getReturnType();
         assert returnType != null : "function is not initialized: " + function;
         List<ValueParameterDescriptor> valueParameters = function.getValueParameters();
diff --git a/compiler/frontend.java/src/org/jetbrains/kotlin/load/java/sam/SingleAbstractMethodUtils.kt b/compiler/frontend.java/src/org/jetbrains/kotlin/load/java/sam/SingleAbstractMethodUtils.kt
index 7d1d8c00a49..a25fd2ae229 100644
--- a/compiler/frontend.java/src/org/jetbrains/kotlin/load/java/sam/SingleAbstractMethodUtils.kt
+++ b/compiler/frontend.java/src/org/jetbrains/kotlin/load/java/sam/SingleAbstractMethodUtils.kt
@@ -16,7 +16,7 @@
 
 package org.jetbrains.kotlin.load.java.sam
 
-import org.jetbrains.kotlin.types.KotlinType
+import org.jetbrains.kotlin.types.SimpleType
 import org.jetbrains.kotlin.types.Variance
 import org.jetbrains.kotlin.types.replace
 import org.jetbrains.kotlin.types.typeUtil.asTypeProjection
@@ -31,7 +31,7 @@ import org.jetbrains.kotlin.utils.addToStdlib.check
 // - Otherwise no non-projection parametrization exists for such 'samType'
 //
 // See Non-wildcard parametrization in JLS 8 p.9.9 for clarification
-internal fun nonProjectionParametrization(samType: KotlinType): KotlinType? {
+internal fun nonProjectionParametrization(samType: SimpleType): SimpleType? {
     if (samType.arguments.none { it.projectionKind != Variance.INVARIANT }) return samType
     val parameters = samType.constructor.parameters
     val parametersSet = parameters.toSet()
diff --git a/core/descriptor.loader.java/src/org/jetbrains/kotlin/load/java/components/SamConversionResolver.kt b/core/descriptor.loader.java/src/org/jetbrains/kotlin/load/java/components/SamConversionResolver.kt
index 12e5c947b11..2ebd3f2a740 100644
--- a/core/descriptor.loader.java/src/org/jetbrains/kotlin/load/java/components/SamConversionResolver.kt
+++ b/core/descriptor.loader.java/src/org/jetbrains/kotlin/load/java/components/SamConversionResolver.kt
@@ -21,18 +21,18 @@ import org.jetbrains.kotlin.descriptors.DeclarationDescriptor
 import org.jetbrains.kotlin.descriptors.FunctionDescriptor
 import org.jetbrains.kotlin.load.java.descriptors.JavaClassDescriptor
 import org.jetbrains.kotlin.load.java.descriptors.SamConstructorDescriptor
-import org.jetbrains.kotlin.types.KotlinType
+import org.jetbrains.kotlin.types.SimpleType
 
 interface SamConversionResolver {
     companion object EMPTY : SamConversionResolver {
         override fun <D : FunctionDescriptor> resolveSamAdapter(original: D) = null
         override fun resolveSamConstructor(constructorOwner: DeclarationDescriptor, classifier: () -> ClassifierDescriptor?) = null
-        override fun resolveFunctionTypeIfSamInterface(classDescriptor: JavaClassDescriptor): KotlinType? = null
+        override fun resolveFunctionTypeIfSamInterface(classDescriptor: JavaClassDescriptor): SimpleType? = null
     }
 
     fun resolveSamConstructor(constructorOwner: DeclarationDescriptor, classifier: () -> ClassifierDescriptor?): SamConstructorDescriptor?
 
     fun <D : FunctionDescriptor> resolveSamAdapter(original: D): D?
 
-    fun resolveFunctionTypeIfSamInterface(classDescriptor: JavaClassDescriptor): KotlinType?
+    fun resolveFunctionTypeIfSamInterface(classDescriptor: JavaClassDescriptor): SimpleType?
 }
diff --git a/core/descriptor.loader.java/src/org/jetbrains/kotlin/load/java/descriptors/JavaClassDescriptor.java b/core/descriptor.loader.java/src/org/jetbrains/kotlin/load/java/descriptors/JavaClassDescriptor.java
index d3f9c94ddce..203a898f5fe 100644
--- a/core/descriptor.loader.java/src/org/jetbrains/kotlin/load/java/descriptors/JavaClassDescriptor.java
+++ b/core/descriptor.loader.java/src/org/jetbrains/kotlin/load/java/descriptors/JavaClassDescriptor.java
@@ -18,9 +18,9 @@ package org.jetbrains.kotlin.load.java.descriptors;
 
 import org.jetbrains.annotations.Nullable;
 import org.jetbrains.kotlin.descriptors.ClassDescriptor;
-import org.jetbrains.kotlin.types.KotlinType;
+import org.jetbrains.kotlin.types.SimpleType;
 
 public interface JavaClassDescriptor extends ClassDescriptor {
     @Nullable
-    KotlinType getFunctionTypeForSamInterface();
+    SimpleType getFunctionTypeForSamInterface();
 }
diff --git a/core/descriptor.loader.java/src/org/jetbrains/kotlin/load/java/lazy/descriptors/LazyJavaClassDescriptor.kt b/core/descriptor.loader.java/src/org/jetbrains/kotlin/load/java/lazy/descriptors/LazyJavaClassDescriptor.kt
index fbc0c6c26f7..bfd73e258ed 100644
--- a/core/descriptor.loader.java/src/org/jetbrains/kotlin/load/java/lazy/descriptors/LazyJavaClassDescriptor.kt
+++ b/core/descriptor.loader.java/src/org/jetbrains/kotlin/load/java/lazy/descriptors/LazyJavaClassDescriptor.kt
@@ -126,7 +126,7 @@ class LazyJavaClassDescriptor(
 
     override fun getDeclaredTypeParameters() = declaredParameters()
 
-    override fun getFunctionTypeForSamInterface(): KotlinType? = functionTypeForSamInterface()
+    override fun getFunctionTypeForSamInterface(): SimpleType? = functionTypeForSamInterface()
 
     override fun isCompanionObject() = false