diff --git a/compiler/ir/ir.psi2ir/src/org/jetbrains/kotlin/psi2ir/generators/BranchingExpressionGenerator.kt b/compiler/ir/ir.psi2ir/src/org/jetbrains/kotlin/psi2ir/generators/BranchingExpressionGenerator.kt
index c7c246bd01c..ff3e9eddcda 100644
--- a/compiler/ir/ir.psi2ir/src/org/jetbrains/kotlin/psi2ir/generators/BranchingExpressionGenerator.kt
+++ b/compiler/ir/ir.psi2ir/src/org/jetbrains/kotlin/psi2ir/generators/BranchingExpressionGenerator.kt
@@ -205,12 +205,22 @@ class BranchingExpressionGenerator(statementGenerator: StatementGenerator) : Sta
         val typeOperand = getOrFail(BindingContext.TYPE, ktCondition.typeReference)
         val irTypeOperand = typeOperand.toIrType()
         val typeSymbol = irTypeOperand.classifierOrNull ?: throw AssertionError("Not a classifier type: $typeOperand")
-        return IrTypeOperatorCallImpl(
+        val irInstanceOf = IrTypeOperatorCallImpl(
             ktCondition.startOffset, ktCondition.endOffset,
             context.irBuiltIns.booleanType,
-            IrTypeOperator.INSTANCEOF, irTypeOperand, typeSymbol,
+            IrTypeOperator.INSTANCEOF,
+            irTypeOperand, typeSymbol,
             irSubject.defaultLoad()
         )
+        return if (ktCondition.isNegated)
+            IrUnaryPrimitiveImpl(
+                ktCondition.startOffset, ktCondition.endOffset,
+                context.irBuiltIns.booleanType,
+                IrStatementOrigin.EXCL, context.irBuiltIns.booleanNotSymbol,
+                irInstanceOf
+            )
+        else
+            irInstanceOf
     }
 
     private fun generateInRangeCondition(irSubject: IrVariable, ktCondition: KtWhenConditionInRange): IrExpression {
diff --git a/compiler/testData/ir/irText/expressions/floatingPointComparisons/whenByFloatingPoint.txt b/compiler/testData/ir/irText/expressions/floatingPointComparisons/whenByFloatingPoint.txt
index b4f5194c77a..7c292fd3d9f 100644
--- a/compiler/testData/ir/irText/expressions/floatingPointComparisons/whenByFloatingPoint.txt
+++ b/compiler/testData/ir/irText/expressions/floatingPointComparisons/whenByFloatingPoint.txt
@@ -75,9 +75,10 @@ FILE fqName:<root> fileName:/whenByFloatingPoint.kt
             GET_VAR 'value-parameter x: Any' type=kotlin.Any origin=null
           WHEN type=kotlin.Int origin=WHEN
             BRANCH
-              if: TYPE_OP type=kotlin.Boolean origin=INSTANCEOF typeOperand=kotlin.Double
-                typeOperand: CLASS IR_EXTERNAL_DECLARATION_STUB CLASS name:Double modality:FINAL visibility:public flags: superTypes:[kotlin.Number; kotlin.Comparable<kotlin.Double>; java.io.Serializable]
-                GET_VAR 'tmp0_subject: Any' type=kotlin.Any origin=null
+              if: CALL 'NOT(Boolean): Boolean' type=kotlin.Boolean origin=EXCL
+                arg0: TYPE_OP type=kotlin.Boolean origin=INSTANCEOF typeOperand=kotlin.Double
+                  typeOperand: CLASS IR_EXTERNAL_DECLARATION_STUB CLASS name:Double modality:FINAL visibility:public flags: superTypes:[kotlin.Number; kotlin.Comparable<kotlin.Double>; java.io.Serializable]
+                  GET_VAR 'tmp0_subject: Any' type=kotlin.Any origin=null
               then: CONST Int type=kotlin.Int value=-1
             BRANCH
               if: CALL 'ieee754equals(Double?, Double?): Boolean' type=kotlin.Boolean origin=EQEQ
diff --git a/compiler/testData/ir/irText/expressions/when.kt b/compiler/testData/ir/irText/expressions/when.kt
index fb4c3d2243c..5c98ee339ad 100644
--- a/compiler/testData/ir/irText/expressions/when.kt
+++ b/compiler/testData/ir/irText/expressions/when.kt
@@ -7,6 +7,7 @@ fun testWithSubject(x: Any?) =
             null -> "null"
             A -> "A"
             is String -> "String"
+            !is Number -> "!Number"
             in setOf<Nothing>() -> "nothingness?"
             else -> "something"
         }
@@ -16,6 +17,7 @@ fun test(x: Any?) =
             x == null -> "null"
             x == A -> "A"
             x is String -> "String"
+            x !is Number -> "!Number"
             x in setOf<Nothing>() -> "nothingness?"
             else -> "something"
         }
diff --git a/compiler/testData/ir/irText/expressions/when.txt b/compiler/testData/ir/irText/expressions/when.txt
index 9f104dfc978..7abb99d7b35 100644
--- a/compiler/testData/ir/irText/expressions/when.txt
+++ b/compiler/testData/ir/irText/expressions/when.txt
@@ -42,11 +42,19 @@ FILE fqName:<root> fileName:/when.kt
                 GET_VAR 'tmp0_subject: Any?' type=kotlin.Any? origin=null
               then: CONST String type=kotlin.String value=String
             BRANCH
-              if: CALL 'contains(Any) on Iterable<Any>: Boolean' type=kotlin.Boolean origin=IN
-                <T>: kotlin.Any
+              if: CALL 'NOT(Boolean): Boolean' type=kotlin.Boolean origin=EXCL
+                arg0: TYPE_OP type=kotlin.Boolean origin=INSTANCEOF typeOperand=kotlin.Number
+                  typeOperand: CLASS IR_EXTERNAL_DECLARATION_STUB CLASS name:Number modality:ABSTRACT visibility:public flags: superTypes:[kotlin.Any; java.io.Serializable]
+                  GET_VAR 'tmp0_subject: Any?' type=kotlin.Any? origin=null
+              then: CONST String type=kotlin.String value=!Number
+            BRANCH
+              if: CALL 'contains(Number) on Iterable<Number>: Boolean' type=kotlin.Boolean origin=IN
+                <T>: kotlin.Number
                 $receiver: CALL 'setOf(): Set<Nothing>' type=kotlin.collections.Set<kotlin.Nothing> origin=null
                   <T>: kotlin.Nothing
-                element: GET_VAR 'tmp0_subject: Any?' type=kotlin.Any? origin=null
+                element: TYPE_OP type=kotlin.Number origin=IMPLICIT_CAST typeOperand=kotlin.Number
+                  typeOperand: CLASS IR_EXTERNAL_DECLARATION_STUB CLASS name:Number modality:ABSTRACT visibility:public flags: superTypes:[kotlin.Any; java.io.Serializable]
+                  GET_VAR 'tmp0_subject: Any?' type=kotlin.Any? origin=null
               then: CONST String type=kotlin.String value=nothingness?
             BRANCH
               if: CONST Boolean type=kotlin.Boolean value=true
@@ -72,11 +80,18 @@ FILE fqName:<root> fileName:/when.kt
               GET_VAR 'value-parameter x: Any?' type=kotlin.Any? origin=null
             then: CONST String type=kotlin.String value=String
           BRANCH
-            if: CALL 'contains(Any) on Iterable<Any>: Boolean' type=kotlin.Boolean origin=IN
-              <T>: kotlin.Any
+            if: TYPE_OP type=kotlin.Boolean origin=NOT_INSTANCEOF typeOperand=kotlin.Number
+              typeOperand: CLASS IR_EXTERNAL_DECLARATION_STUB CLASS name:Number modality:ABSTRACT visibility:public flags: superTypes:[kotlin.Any; java.io.Serializable]
+              GET_VAR 'value-parameter x: Any?' type=kotlin.Any? origin=null
+            then: CONST String type=kotlin.String value=!Number
+          BRANCH
+            if: CALL 'contains(Number) on Iterable<Number>: Boolean' type=kotlin.Boolean origin=IN
+              <T>: kotlin.Number
               $receiver: CALL 'setOf(): Set<Nothing>' type=kotlin.collections.Set<kotlin.Nothing> origin=null
                 <T>: kotlin.Nothing
-              element: GET_VAR 'value-parameter x: Any?' type=kotlin.Any? origin=null
+              element: TYPE_OP type=kotlin.Number origin=IMPLICIT_CAST typeOperand=kotlin.Number
+                typeOperand: CLASS IR_EXTERNAL_DECLARATION_STUB CLASS name:Number modality:ABSTRACT visibility:public flags: superTypes:[kotlin.Any; java.io.Serializable]
+                GET_VAR 'value-parameter x: Any?' type=kotlin.Any? origin=null
             then: CONST String type=kotlin.String value=nothingness?
           BRANCH
             if: CONST Boolean type=kotlin.Boolean value=true
diff --git a/compiler/testData/ir/irText/expressions/whenWithSubjectVariable.txt b/compiler/testData/ir/irText/expressions/whenWithSubjectVariable.txt
index 568444cb7d6..b6325606c7d 100644
--- a/compiler/testData/ir/irText/expressions/whenWithSubjectVariable.txt
+++ b/compiler/testData/ir/irText/expressions/whenWithSubjectVariable.txt
@@ -24,9 +24,10 @@ FILE fqName:<root> fileName:/whenWithSubjectVariable.kt
                   typeOperand: CLASS IR_EXTERNAL_DECLARATION_STUB CLASS name:String modality:FINAL visibility:public flags: superTypes:[kotlin.Comparable<kotlin.String>; kotlin.CharSequence; java.io.Serializable]
                   GET_VAR 'y: Any' type=kotlin.Any origin=null
             BRANCH
-              if: TYPE_OP type=kotlin.Boolean origin=INSTANCEOF typeOperand=kotlin.Int
-                typeOperand: CLASS IR_EXTERNAL_DECLARATION_STUB CLASS name:Int modality:FINAL visibility:public flags: superTypes:[kotlin.Number; kotlin.Comparable<kotlin.Int>; java.io.Serializable]
-                GET_VAR 'y: Any' type=kotlin.Any origin=null
+              if: CALL 'NOT(Boolean): Boolean' type=kotlin.Boolean origin=EXCL
+                arg0: TYPE_OP type=kotlin.Boolean origin=INSTANCEOF typeOperand=kotlin.Int
+                  typeOperand: CLASS IR_EXTERNAL_DECLARATION_STUB CLASS name:Int modality:FINAL visibility:public flags: superTypes:[kotlin.Number; kotlin.Comparable<kotlin.Int>; java.io.Serializable]
+                  GET_VAR 'y: Any' type=kotlin.Any origin=null
               then: CONST Int type=kotlin.Int value=2
             BRANCH
               if: CALL 'contains(Int): Boolean' type=kotlin.Boolean origin=IN