diff --git a/idea/src/org/jetbrains/kotlin/idea/refactoring/introduce/extractionEngine/extractableAnalysisUtil.kt b/idea/src/org/jetbrains/kotlin/idea/refactoring/introduce/extractionEngine/extractableAnalysisUtil.kt
index 0af7fe15f79..dce71379e7e 100644
--- a/idea/src/org/jetbrains/kotlin/idea/refactoring/introduce/extractionEngine/extractableAnalysisUtil.kt
+++ b/idea/src/org/jetbrains/kotlin/idea/refactoring/introduce/extractionEngine/extractableAnalysisUtil.kt
@@ -541,23 +541,26 @@ private class MutableParameter(
 
         val typePredicate = and(typePredicates)
 
-        val typeList = if (defaultType.isNullabilityFlexible()) {
-            val bounds = defaultType.getCapability(javaClass<Flexibility>())
-            if (typePredicate(bounds!!.upperBound)) arrayListOf(bounds.upperBound, bounds.lowerBound) else arrayListOf(bounds.lowerBound)
+        val typeSet = if (defaultType.isFlexible()) {
+            val bounds = defaultType.getCapability(javaClass<Flexibility>())!!
+            LinkedHashSet<JetType>().apply {
+                if (typePredicate(bounds.upperBound)) add(bounds.upperBound)
+                if (typePredicate(bounds.lowerBound)) add(bounds.lowerBound)
+            }
         }
-        else arrayListOf(defaultType)
+        else linkedSetOf(defaultType)
 
-        val addNullableTypes = typeList.size() > 1
+        val addNullableTypes = defaultType.isNullabilityFlexible() && typeSet.size() > 1
         val superTypes = TypeUtils.getAllSupertypes(defaultType).filter(typePredicate)
 
         for (superType in superTypes) {
             if (addNullableTypes) {
-                typeList.add(superType.makeNullable())
+                typeSet.add(superType.makeNullable())
             }
-            typeList.add(superType)
+            typeSet.add(superType)
         }
 
-        typeList
+        typeSet.toList()
     }
 
     override fun getParameterTypeCandidates(allowSpecialClassNames: Boolean): List<JetType> {
diff --git a/idea/testData/refactoring/extractFunction/parameters/candidateTypes/mutablyFlexibleType.java b/idea/testData/refactoring/extractFunction/parameters/candidateTypes/mutablyFlexibleType.java
new file mode 100644
index 00000000000..54022cc9ba7
--- /dev/null
+++ b/idea/testData/refactoring/extractFunction/parameters/candidateTypes/mutablyFlexibleType.java
@@ -0,0 +1,7 @@
+import java.util.*;
+
+class J {
+    public List<String> getData() {
+        return new ArrayList<String>();
+    }
+}
\ No newline at end of file
diff --git a/idea/testData/refactoring/extractFunction/parameters/candidateTypes/mutablyFlexibleType.kt b/idea/testData/refactoring/extractFunction/parameters/candidateTypes/mutablyFlexibleType.kt
new file mode 100644
index 00000000000..2c1ef2084b2
--- /dev/null
+++ b/idea/testData/refactoring/extractFunction/parameters/candidateTypes/mutablyFlexibleType.kt
@@ -0,0 +1,8 @@
+// WITH_RUNTIME
+// PARAM_DESCRIPTOR: val data: (kotlin.MutableList<(kotlin.String..kotlin.String?)>..kotlin.List<(kotlin.String..kotlin.String?)>) defined in test
+// PARAM_TYPES: kotlin.List<(kotlin.String..kotlin.String?)>, kotlin.MutableList<(kotlin.String..kotlin.String?)>, kotlin.MutableCollection<(kotlin.String..kotlin.String?)>, kotlin.Collection<(kotlin.String..kotlin.String?)>
+fun test(): Boolean {
+    val j: J? = null
+    val data = j?.getData() ?: return false
+    return <selection>data.contains("foo")</selection>
+}
\ No newline at end of file
diff --git a/idea/testData/refactoring/extractFunction/parameters/candidateTypes/mutablyFlexibleType.kt.after b/idea/testData/refactoring/extractFunction/parameters/candidateTypes/mutablyFlexibleType.kt.after
new file mode 100644
index 00000000000..d4dc8ce0e3b
--- /dev/null
+++ b/idea/testData/refactoring/extractFunction/parameters/candidateTypes/mutablyFlexibleType.kt.after
@@ -0,0 +1,10 @@
+// WITH_RUNTIME
+// PARAM_DESCRIPTOR: val data: (kotlin.MutableList<(kotlin.String..kotlin.String?)>..kotlin.List<(kotlin.String..kotlin.String?)>) defined in test
+// PARAM_TYPES: kotlin.List<(kotlin.String..kotlin.String?)>, kotlin.MutableList<(kotlin.String..kotlin.String?)>, kotlin.MutableCollection<(kotlin.String..kotlin.String?)>, kotlin.Collection<(kotlin.String..kotlin.String?)>
+fun test(): Boolean {
+    val j: J? = null
+    val data = j?.getData() ?: return false
+    return b(data)
+}
+
+private fun b(data: List<String>) = data.contains("foo")
\ No newline at end of file
diff --git a/idea/tests/org/jetbrains/kotlin/idea/refactoring/introduce/JetExtractionTestGenerated.java b/idea/tests/org/jetbrains/kotlin/idea/refactoring/introduce/JetExtractionTestGenerated.java
index 1d659de3d14..8a115ac8f4d 100644
--- a/idea/tests/org/jetbrains/kotlin/idea/refactoring/introduce/JetExtractionTestGenerated.java
+++ b/idea/tests/org/jetbrains/kotlin/idea/refactoring/introduce/JetExtractionTestGenerated.java
@@ -1802,6 +1802,12 @@ public class JetExtractionTestGenerated extends AbstractJetExtractionTest {
                     doExtractFunctionTest(fileName);
                 }
 
+                @TestMetadata("mutablyFlexibleType.kt")
+                public void testMutablyFlexibleType() throws Exception {
+                    String fileName = JetTestUtils.navigationMetadata("idea/testData/refactoring/extractFunction/parameters/candidateTypes/mutablyFlexibleType.kt");
+                    doExtractFunctionTest(fileName);
+                }
+
                 @TestMetadata("nonNullableTypes.kt")
                 public void testNonNullableTypes() throws Exception {
                     String fileName = JetTestUtils.navigationMetadata("idea/testData/refactoring/extractFunction/parameters/candidateTypes/nonNullableTypes.kt");