diff --git a/src/main/kotlin/com/github/suusan2go/kotlinfillclass/inspections/FillClassInspection.kt b/src/main/kotlin/com/github/suusan2go/kotlinfillclass/inspections/FillClassInspection.kt
index f8427aa..8961eb0 100644
--- a/src/main/kotlin/com/github/suusan2go/kotlinfillclass/inspections/FillClassInspection.kt
+++ b/src/main/kotlin/com/github/suusan2go/kotlinfillclass/inspections/FillClassInspection.kt
@@ -12,11 +12,10 @@ import com.intellij.psi.PsiDocumentManager
 import com.intellij.psi.PsiElement
 import org.jetbrains.kotlin.builtins.KotlinBuiltIns
 import org.jetbrains.kotlin.builtins.isFunctionType
-import org.jetbrains.kotlin.descriptors.CallableDescriptor
 import org.jetbrains.kotlin.descriptors.ClassConstructorDescriptor
 import org.jetbrains.kotlin.descriptors.ClassKind
+import org.jetbrains.kotlin.descriptors.FunctionDescriptor
 import org.jetbrains.kotlin.descriptors.Modality
-import org.jetbrains.kotlin.descriptors.SimpleFunctionDescriptor
 import org.jetbrains.kotlin.descriptors.ValueParameterDescriptor
 import org.jetbrains.kotlin.idea.caches.resolve.resolveToCall
 import org.jetbrains.kotlin.idea.core.CollectingNameValidator
@@ -80,11 +79,11 @@ class FillClassInspection(
     }
 }
 
-private fun KtValueArgumentList.descriptor(): CallableDescriptor? {
+private fun KtValueArgumentList.descriptor(): FunctionDescriptor? {
     val calleeExpression = getStrictParentOfType<KtCallElement>()?.calleeExpression ?: return null
-    val descriptor = calleeExpression.resolveToCall()?.resultingDescriptor
+    val descriptor = calleeExpression.resolveToCall()?.resultingDescriptor as? FunctionDescriptor ?: return null
     if (descriptor is JavaCallableMemberDescriptor) return null
-    return descriptor.takeIf { it is ClassConstructorDescriptor || it is SimpleFunctionDescriptor }
+    return descriptor
 }
 
 class FillClassFix(
diff --git a/src/test/kotlin/com/github/suusan2go/kotlinfillclass/inspections/FillClassInspectionTest.kt b/src/test/kotlin/com/github/suusan2go/kotlinfillclass/inspections/FillClassInspectionTest.kt
index 07ca1ad..f6e6de8 100644
--- a/src/test/kotlin/com/github/suusan2go/kotlinfillclass/inspections/FillClassInspectionTest.kt
+++ b/src/test/kotlin/com/github/suusan2go/kotlinfillclass/inspections/FillClassInspectionTest.kt
@@ -189,6 +189,52 @@ class FillClassInspectionTest : BasePlatformTestCase() {
         )
     }
 
+    fun `test extension function`() {
+        doAvailableTest(
+            """
+            class Foo
+            fun Foo.foo(x: Int, y: Int) {}
+            fun test() {
+                Foo().foo(<caret>)
+            }
+        """,
+            """
+            class Foo
+            fun Foo.foo(x: Int, y: Int) {}
+            fun test() {
+                Foo().foo(x = 0, y = 0)
+            }
+        """,
+            "Fill function"
+        )
+    }
+
+    fun `test imported extension function`() {
+        doAvailableTest(
+            """
+            import Bar.foo
+            class Foo
+            object Bar {
+                fun Foo.foo(x: Int, y: Int) {}
+            }
+            fun test() {
+                Foo().foo(<caret>)
+            }
+        """,
+            """
+            import Bar.foo
+            class Foo
+            object Bar {
+                fun Foo.foo(x: Int, y: Int) {}
+            }
+            fun test() {
+                Foo().foo(x = 0, y = 0)
+            }
+        """,
+            "Fill function"
+        )
+    }
+
     fun `test fill class constructor without default values`() {
         doAvailableTest(
             """