diff --git a/compiler/frontend/src/org/jetbrains/kotlin/diagnostics/Errors.java b/compiler/frontend/src/org/jetbrains/kotlin/diagnostics/Errors.java
index cba774061c4..f4602f1ecab 100644
--- a/compiler/frontend/src/org/jetbrains/kotlin/diagnostics/Errors.java
+++ b/compiler/frontend/src/org/jetbrains/kotlin/diagnostics/Errors.java
@@ -800,6 +800,8 @@ public interface Errors {
 
     DiagnosticFactory2<KtElement, KotlinType, KotlinType> INCOMPATIBLE_ENUM_COMPARISON =
             DiagnosticFactory2.create(WARNING);
+    DiagnosticFactory2<KtElement, KotlinType, KotlinType> INCOMPATIBLE_ENUM_COMPARISON_ERROR =
+            DiagnosticFactory2.create(ERROR);
 
     DiagnosticFactory1<KtExpression, KotlinType> HAS_NEXT_MISSING = DiagnosticFactory1.create(ERROR);
     DiagnosticFactory1<KtExpression, KotlinType> HAS_NEXT_FUNCTION_AMBIGUITY = DiagnosticFactory1.create(ERROR);
diff --git a/compiler/frontend/src/org/jetbrains/kotlin/diagnostics/rendering/DefaultErrorMessages.java b/compiler/frontend/src/org/jetbrains/kotlin/diagnostics/rendering/DefaultErrorMessages.java
index 42da0f262c3..0a933eb0ea8 100644
--- a/compiler/frontend/src/org/jetbrains/kotlin/diagnostics/rendering/DefaultErrorMessages.java
+++ b/compiler/frontend/src/org/jetbrains/kotlin/diagnostics/rendering/DefaultErrorMessages.java
@@ -741,6 +741,7 @@ public class DefaultErrorMessages {
         }, RENDER_TYPE, RENDER_TYPE);
 
         MAP.put(INCOMPATIBLE_ENUM_COMPARISON, "Comparison of incompatible enums ''{0}'' and ''{1}'' is always unsuccessful", RENDER_TYPE, RENDER_TYPE);
+        MAP.put(INCOMPATIBLE_ENUM_COMPARISON_ERROR, "Comparison of incompatible enums ''{0}'' and ''{1}'' is always unsuccessful", RENDER_TYPE, RENDER_TYPE);
 
         MAP.put(SENSELESS_COMPARISON, "Condition ''{0}'' is always ''{1}''", ELEMENT_TEXT, TO_STRING);
         MAP.put(SENSELESS_NULL_IN_WHEN, "Expression under 'when' is never equal to null");
diff --git a/compiler/frontend/src/org/jetbrains/kotlin/types/TypeIntersector.java b/compiler/frontend/src/org/jetbrains/kotlin/types/TypeIntersector.java
index af0743daa1b..18616c7901d 100644
--- a/compiler/frontend/src/org/jetbrains/kotlin/types/TypeIntersector.java
+++ b/compiler/frontend/src/org/jetbrains/kotlin/types/TypeIntersector.java
@@ -28,7 +28,6 @@ import org.jetbrains.kotlin.resolve.calls.inference.CallHandle;
 import org.jetbrains.kotlin.resolve.calls.inference.ConstraintSystem;
 import org.jetbrains.kotlin.resolve.calls.inference.ConstraintSystemBuilderImpl;
 import org.jetbrains.kotlin.types.checker.KotlinTypeChecker;
-import org.jetbrains.kotlin.types.typeUtil.TypeUtilsKt;
 
 import java.util.*;
 
@@ -41,11 +40,6 @@ public class TypeIntersector {
         return intersectTypes(new LinkedHashSet<>(Arrays.asList(typeA, typeB))) == null;
     }
 
-    public static boolean isIncompatibleEnums(@NotNull KotlinType typeA, @NotNull KotlinType typeB) {
-        if (!TypeUtilsKt.isEnum(typeA) || !TypeUtilsKt.isEnum(typeB)) return false;
-        return !typeA.getConstructor().equals(typeB.getConstructor());
-    }
-
     @Nullable
     public static KotlinType intersectTypes(@NotNull Collection<KotlinType> types) {
         assert !types.isEmpty() : "Attempting to intersect empty collection of types, this case should be dealt with on the call site.";
diff --git a/compiler/frontend/src/org/jetbrains/kotlin/types/enumCompatibilityChecker.kt b/compiler/frontend/src/org/jetbrains/kotlin/types/enumCompatibilityChecker.kt
new file mode 100644
index 00000000000..f66fbaedff2
--- /dev/null
+++ b/compiler/frontend/src/org/jetbrains/kotlin/types/enumCompatibilityChecker.kt
@@ -0,0 +1,49 @@
+/*
+ * Copyright 2010-2019 JetBrains s.r.o. Use of this source code is governed by the Apache 2.0 license
+ * that can be found in the license/LICENSE.txt file.
+ */
+
+package org.jetbrains.kotlin.types
+
+import org.jetbrains.kotlin.config.LanguageFeature
+import org.jetbrains.kotlin.descriptors.ClassDescriptor
+import org.jetbrains.kotlin.descriptors.TypeParameterDescriptor
+import org.jetbrains.kotlin.diagnostics.Errors
+import org.jetbrains.kotlin.psi.KtElement
+import org.jetbrains.kotlin.resolve.DescriptorUtils
+import org.jetbrains.kotlin.types.expressions.ExpressionTypingContext
+import org.jetbrains.kotlin.types.typeUtil.*
+
+fun checkEnumsForCompatibility(context: ExpressionTypingContext, reportOn: KtElement, typeA: KotlinType, typeB: KotlinType) {
+    if (isIncompatibleEnums(typeA, typeB)) {
+        val diagnostic = if (context.languageVersionSettings.supportsFeature(LanguageFeature.ProhibitComparisonOfIncompatibleEnums)) {
+            Errors.INCOMPATIBLE_ENUM_COMPARISON_ERROR
+        } else {
+            Errors.INCOMPATIBLE_ENUM_COMPARISON
+        }
+
+        context.trace.report(diagnostic.on(reportOn, typeA, typeB))
+    }
+}
+
+private fun isIncompatibleEnums(typeA: KotlinType, typeB: KotlinType): Boolean {
+    if (!typeA.isEnum() && !typeB.isEnum()) return false
+    if (TypeUtils.isNullableType(typeA) && TypeUtils.isNullableType(typeB)) return false
+
+    // TODO: remove this line once KT-30266 will be fixed
+    // For now, this check is needed as isSubClass contains bug wrt Nothing
+    if (typeA.isNothingOrNullableNothing() || typeB.isNothingOrNullableNothing()) return false
+
+    val representativeTypeA = typeA.representativeTypeForTypeParameter()
+    val representativeTypeB = typeB.representativeTypeForTypeParameter()
+
+    val classA = representativeTypeA.constructor.declarationDescriptor as? ClassDescriptor ?: return false
+    val classB = representativeTypeB.constructor.declarationDescriptor as? ClassDescriptor ?: return false
+
+    return !DescriptorUtils.isSubclass(classA, classB) && !DescriptorUtils.isSubclass(classB, classA)
+}
+
+private fun KotlinType.representativeTypeForTypeParameter(): KotlinType {
+    val descriptor = constructor.declarationDescriptor
+    return if (descriptor is TypeParameterDescriptor) descriptor.representativeUpperBound else this
+}
diff --git a/compiler/frontend/src/org/jetbrains/kotlin/types/expressions/BasicExpressionTypingVisitor.java b/compiler/frontend/src/org/jetbrains/kotlin/types/expressions/BasicExpressionTypingVisitor.java
index 1aa940ff059..084381c0d47 100644
--- a/compiler/frontend/src/org/jetbrains/kotlin/types/expressions/BasicExpressionTypingVisitor.java
+++ b/compiler/frontend/src/org/jetbrains/kotlin/types/expressions/BasicExpressionTypingVisitor.java
@@ -1430,10 +1430,10 @@ public class BasicExpressionTypingVisitor extends ExpressionTypingVisitor {
             if (rightType != null) {
                 if (TypeIntersector.isIntersectionEmpty(leftType, rightType)) {
                     context.trace.report(EQUALITY_NOT_APPLICABLE.on(expression, expression.getOperationReference(), leftType, rightType));
+                } else {
+                    EnumCompatibilityCheckerKt.checkEnumsForCompatibility(context, expression, leftType, rightType);
                 }
-                else if (TypeIntersector.isIncompatibleEnums(leftType, rightType)) {
-                    context.trace.report(INCOMPATIBLE_ENUM_COMPARISON.on(expression, leftType, rightType));
-                }
+
 
                 SenselessComparisonChecker.checkSenselessComparisonWithNull(
                         expression, left, right, context,
diff --git a/compiler/frontend/src/org/jetbrains/kotlin/types/expressions/PatternMatchingTypingVisitor.kt b/compiler/frontend/src/org/jetbrains/kotlin/types/expressions/PatternMatchingTypingVisitor.kt
index 743f4fb4d01..a66225e067a 100644
--- a/compiler/frontend/src/org/jetbrains/kotlin/types/expressions/PatternMatchingTypingVisitor.kt
+++ b/compiler/frontend/src/org/jetbrains/kotlin/types/expressions/PatternMatchingTypingVisitor.kt
@@ -684,9 +684,7 @@ class PatternMatchingTypingVisitor internal constructor(facade: ExpressionTyping
             return
         }
 
-        if (TypeIntersector.isIncompatibleEnums(type, subjectType)) {
-            context.trace.report(INCOMPATIBLE_ENUM_COMPARISON.on(reportErrorOn, subjectType, type))
-        }
+        checkEnumsForCompatibility(context, reportErrorOn, type, subjectType)
 
         // check if the pattern is essentially a 'null' expression
         if (KotlinBuiltIns.isNullableNothing(type) && !TypeUtils.isNullableType(subjectType)) {
diff --git a/compiler/testData/diagnostics/tests/enum/incompatibleEnums.kt b/compiler/testData/diagnostics/tests/enum/incompatibleEnums.kt
index 7be3faad7b1..784285f7a82 100644
--- a/compiler/testData/diagnostics/tests/enum/incompatibleEnums.kt
+++ b/compiler/testData/diagnostics/tests/enum/incompatibleEnums.kt
@@ -1,3 +1,5 @@
+// !LANGUAGE: -ProhibitComparisonOfIncompatibleEnums
+
 enum class E1 {
     A, B
 }
@@ -56,3 +58,88 @@ fun foo3(e1: Enum<E1>, e2: Enum<E2>, e: Enum<*>) {
         else -> {}
     }
 }
+
+interface MyInterface
+open class MyOpenClass
+
+fun foo4(e1: E1, i: MyInterface, c: MyOpenClass) {
+    <!INCOMPATIBLE_ENUM_COMPARISON!>e1 == i<!>
+    <!INCOMPATIBLE_ENUM_COMPARISON!>i == e1<!>
+
+    <!INCOMPATIBLE_ENUM_COMPARISON!>e1 == c<!>
+    <!INCOMPATIBLE_ENUM_COMPARISON!>c == e1<!>
+
+    when (e1) {
+        <!INCOMPATIBLE_ENUM_COMPARISON!>i<!> -> {}
+        <!INCOMPATIBLE_ENUM_COMPARISON!>c<!> -> {}
+        else -> {}
+    }
+}
+
+enum class E3 : MyInterface { X, Y }
+
+fun foo5(i: MyInterface, a: Any) {
+    E3.X == E3.Y
+    E3.X == i
+    E3.X == a
+}
+
+fun foo6(e1: E1?, e2: E2) {
+    <!SENSELESS_COMPARISON!>E1.A == null<!>
+    <!SENSELESS_COMPARISON!>null == E1.A<!>
+    e1 == null
+    null == e1
+
+    <!INCOMPATIBLE_ENUM_COMPARISON!>e1 == E2.A<!>
+    <!INCOMPATIBLE_ENUM_COMPARISON!>E2.A == e1<!>
+    <!INCOMPATIBLE_ENUM_COMPARISON!>e1 == e2<!>
+    <!INCOMPATIBLE_ENUM_COMPARISON!>e2 == e1<!>
+
+    <!SENSELESS_COMPARISON!>e2 == null<!>
+    <!SENSELESS_COMPARISON!>null == e2<!>
+    <!SENSELESS_COMPARISON!>E1.A == null<!>
+    <!SENSELESS_COMPARISON!>null == E1.A<!>
+}
+
+fun foo7(e1: E1?, e2: E2?) {
+    e1 == e2 // There should be an IDE-inspection for such cases
+}
+
+fun <T> foo8(e1: E1?, e2: E2, t: T) {
+    e1 == t
+    t == e1
+
+    e2 == t
+    t == e2
+
+    E1.A == t
+    t == E1.A
+}
+
+fun <T, K> foo9(e1: E1?, e2: E2, t: T, k: K) where T : MyInterface, T : MyOpenClass, K : MyInterface {
+    <!INCOMPATIBLE_ENUM_COMPARISON!>e1 == t<!>
+    <!INCOMPATIBLE_ENUM_COMPARISON!>t == e1<!>
+
+    <!INCOMPATIBLE_ENUM_COMPARISON!>e2 == t<!>
+    <!INCOMPATIBLE_ENUM_COMPARISON!>t == e2<!>
+
+    <!INCOMPATIBLE_ENUM_COMPARISON!>E1.A == t<!>
+    <!INCOMPATIBLE_ENUM_COMPARISON!>t == E1.A<!>
+
+    <!INCOMPATIBLE_ENUM_COMPARISON!>E3.X == t<!>
+
+    E3.X == k
+    k == E3.X
+}
+
+interface Inv<T>
+
+enum class E4 : Inv<Int> { A }
+
+fun foo10(e4: E4, invString: Inv<String>) {
+    e4 == invString
+    invString == e4
+
+    E4.A == invString
+    invString == E4.A
+}
\ No newline at end of file
diff --git a/compiler/testData/diagnostics/tests/enum/incompatibleEnums.txt b/compiler/testData/diagnostics/tests/enum/incompatibleEnums.txt
index 33d652b54a3..5e46d9fc2e5 100644
--- a/compiler/testData/diagnostics/tests/enum/incompatibleEnums.txt
+++ b/compiler/testData/diagnostics/tests/enum/incompatibleEnums.txt
@@ -1,8 +1,15 @@
 package
 
 public fun foo1(/*0*/ e1: E1, /*1*/ e2: E2): kotlin.Unit
+public fun foo10(/*0*/ e4: E4, /*1*/ invString: Inv<kotlin.String>): kotlin.Unit
 public fun foo2(/*0*/ e1: E1, /*1*/ e2: E2): kotlin.Unit
 public fun foo3(/*0*/ e1: kotlin.Enum<E1>, /*1*/ e2: kotlin.Enum<E2>, /*2*/ e: kotlin.Enum<*>): kotlin.Unit
+public fun foo4(/*0*/ e1: E1, /*1*/ i: MyInterface, /*2*/ c: MyOpenClass): kotlin.Unit
+public fun foo5(/*0*/ i: MyInterface, /*1*/ a: kotlin.Any): kotlin.Unit
+public fun foo6(/*0*/ e1: E1?, /*1*/ e2: E2): kotlin.Unit
+public fun foo7(/*0*/ e1: E1?, /*1*/ e2: E2?): kotlin.Unit
+public fun </*0*/ T> foo8(/*0*/ e1: E1?, /*1*/ e2: E2, /*2*/ t: T): kotlin.Unit
+public fun </*0*/ T : MyInterface, /*1*/ K : MyInterface> foo9(/*0*/ e1: E1?, /*1*/ e2: E2, /*2*/ t: T, /*3*/ k: K): kotlin.Unit where T : MyOpenClass
 
 public final enum class E1 : kotlin.Enum<E1> {
     enum entry A
@@ -45,3 +52,62 @@ public final enum class E2 : kotlin.Enum<E2> {
     public final /*synthesized*/ fun valueOf(/*0*/ value: kotlin.String): E2
     public final /*synthesized*/ fun values(): kotlin.Array<E2>
 }
+
+public final enum class E3 : kotlin.Enum<E3>, MyInterface {
+    enum entry X
+
+    enum entry Y
+
+    private constructor E3()
+    public final override /*1*/ /*fake_override*/ val name: kotlin.String
+    public final override /*1*/ /*fake_override*/ val ordinal: kotlin.Int
+    protected final override /*1*/ /*fake_override*/ fun clone(): kotlin.Any
+    public final override /*1*/ /*fake_override*/ fun compareTo(/*0*/ other: E3): kotlin.Int
+    public final override /*2*/ /*fake_override*/ fun equals(/*0*/ other: kotlin.Any?): kotlin.Boolean
+    protected/*protected and package*/ final override /*1*/ /*fake_override*/ /*isHiddenForResolutionEverywhereBesideSupercalls*/ fun finalize(): kotlin.Unit
+    public final override /*1*/ /*fake_override*/ /*isHiddenForResolutionEverywhereBesideSupercalls*/ fun getDeclaringClass(): java.lang.Class<E3!>!
+    public final override /*2*/ /*fake_override*/ fun hashCode(): kotlin.Int
+    public open override /*2*/ /*fake_override*/ fun toString(): kotlin.String
+
+    // Static members
+    public final /*synthesized*/ fun valueOf(/*0*/ value: kotlin.String): E3
+    public final /*synthesized*/ fun values(): kotlin.Array<E3>
+}
+
+public final enum class E4 : kotlin.Enum<E4>, Inv<kotlin.Int> {
+    enum entry A
+
+    private constructor E4()
+    public final override /*1*/ /*fake_override*/ val name: kotlin.String
+    public final override /*1*/ /*fake_override*/ val ordinal: kotlin.Int
+    protected final override /*1*/ /*fake_override*/ fun clone(): kotlin.Any
+    public final override /*1*/ /*fake_override*/ fun compareTo(/*0*/ other: E4): kotlin.Int
+    public final override /*2*/ /*fake_override*/ fun equals(/*0*/ other: kotlin.Any?): kotlin.Boolean
+    protected/*protected and package*/ final override /*1*/ /*fake_override*/ /*isHiddenForResolutionEverywhereBesideSupercalls*/ fun finalize(): kotlin.Unit
+    public final override /*1*/ /*fake_override*/ /*isHiddenForResolutionEverywhereBesideSupercalls*/ fun getDeclaringClass(): java.lang.Class<E4!>!
+    public final override /*2*/ /*fake_override*/ fun hashCode(): kotlin.Int
+    public open override /*2*/ /*fake_override*/ fun toString(): kotlin.String
+
+    // Static members
+    public final /*synthesized*/ fun valueOf(/*0*/ value: kotlin.String): E4
+    public final /*synthesized*/ fun values(): kotlin.Array<E4>
+}
+
+public interface Inv</*0*/ T> {
+    public open override /*1*/ /*fake_override*/ fun equals(/*0*/ other: kotlin.Any?): kotlin.Boolean
+    public open override /*1*/ /*fake_override*/ fun hashCode(): kotlin.Int
+    public open override /*1*/ /*fake_override*/ fun toString(): kotlin.String
+}
+
+public interface MyInterface {
+    public open override /*1*/ /*fake_override*/ fun equals(/*0*/ other: kotlin.Any?): kotlin.Boolean
+    public open override /*1*/ /*fake_override*/ fun hashCode(): kotlin.Int
+    public open override /*1*/ /*fake_override*/ fun toString(): kotlin.String
+}
+
+public open class MyOpenClass {
+    public constructor MyOpenClass()
+    public open override /*1*/ /*fake_override*/ fun equals(/*0*/ other: kotlin.Any?): kotlin.Boolean
+    public open override /*1*/ /*fake_override*/ fun hashCode(): kotlin.Int
+    public open override /*1*/ /*fake_override*/ fun toString(): kotlin.String
+}
diff --git a/compiler/testData/diagnostics/tests/enum/incompatibleEnums_1_4.kt b/compiler/testData/diagnostics/tests/enum/incompatibleEnums_1_4.kt
new file mode 100644
index 00000000000..ad4afd7ec6a
--- /dev/null
+++ b/compiler/testData/diagnostics/tests/enum/incompatibleEnums_1_4.kt
@@ -0,0 +1,145 @@
+// !LANGUAGE: +ProhibitComparisonOfIncompatibleEnums
+
+enum class E1 {
+    A, B
+}
+
+enum class E2 {
+    A, B
+}
+
+fun foo1(e1: E1, e2: E2) {
+    <!INCOMPATIBLE_ENUM_COMPARISON_ERROR!>e1 == e2<!>
+    <!INCOMPATIBLE_ENUM_COMPARISON_ERROR!>e1 != e2<!>
+
+    <!INCOMPATIBLE_ENUM_COMPARISON_ERROR!>e1 == E2.A<!>
+    <!INCOMPATIBLE_ENUM_COMPARISON_ERROR!>E1.B == e2<!>
+
+    <!INCOMPATIBLE_ENUM_COMPARISON_ERROR!>E1.A == E2.B<!>
+
+    e1 == E1.A
+    E1.A == e1
+    e2 == E2.B
+    E2.B == e2
+}
+
+fun foo2(e1: E1, e2: E2) {
+    when (e1) {
+        E1.A -> {}
+            <!INCOMPATIBLE_ENUM_COMPARISON_ERROR!>E2.A<!> -> {}
+            <!INCOMPATIBLE_ENUM_COMPARISON_ERROR!>E2.B<!> -> {}
+        e1 -> {}
+            <!INCOMPATIBLE_ENUM_COMPARISON_ERROR!>e2<!> -> {}
+        else -> {}
+    }
+}
+
+fun foo3(e1: Enum<E1>, e2: Enum<E2>, e: Enum<*>) {
+    e1 == e
+    e1 == e2
+
+    e1 == E1.A
+    e1 == E2.A
+
+    when (e1) {
+        e1 -> {}
+        e2 -> {}
+        e -> {}
+        E1.A -> {}
+            E2.A -> {}
+        else -> {}
+    }
+
+    when (e) {
+        e -> {}
+        e2 -> {}
+        E1.A -> {}
+        E2.A -> {}
+        else -> {}
+    }
+}
+
+interface MyInterface
+open class MyOpenClass
+
+fun foo4(e1: E1, i: MyInterface, c: MyOpenClass) {
+    <!INCOMPATIBLE_ENUM_COMPARISON_ERROR!>e1 == i<!>
+    <!INCOMPATIBLE_ENUM_COMPARISON_ERROR!>i == e1<!>
+
+    <!INCOMPATIBLE_ENUM_COMPARISON_ERROR!>e1 == c<!>
+    <!INCOMPATIBLE_ENUM_COMPARISON_ERROR!>c == e1<!>
+
+    when (e1) {
+            <!INCOMPATIBLE_ENUM_COMPARISON_ERROR!>i<!> -> {}
+            <!INCOMPATIBLE_ENUM_COMPARISON_ERROR!>c<!> -> {}
+        else -> {}
+    }
+}
+
+enum class E3 : MyInterface { X, Y }
+
+fun foo5(i: MyInterface, a: Any) {
+    E3.X == E3.Y
+    E3.X == i
+    E3.X == a
+}
+
+fun foo6(e1: E1?, e2: E2) {
+    <!SENSELESS_COMPARISON!>E1.A == null<!>
+    <!SENSELESS_COMPARISON!>null == E1.A<!>
+    e1 == null
+    null == e1
+
+    <!INCOMPATIBLE_ENUM_COMPARISON_ERROR!>e1 == E2.A<!>
+    <!INCOMPATIBLE_ENUM_COMPARISON_ERROR!>E2.A == e1<!>
+    <!INCOMPATIBLE_ENUM_COMPARISON_ERROR!>e1 == e2<!>
+    <!INCOMPATIBLE_ENUM_COMPARISON_ERROR!>e2 == e1<!>
+
+    <!SENSELESS_COMPARISON!>e2 == null<!>
+    <!SENSELESS_COMPARISON!>null == e2<!>
+    <!SENSELESS_COMPARISON!>E1.A == null<!>
+    <!SENSELESS_COMPARISON!>null == E1.A<!>
+}
+
+fun foo7(e1: E1?, e2: E2?) {
+    e1 == e2 // There should be an IDE-inspection for such cases
+}
+
+fun <T> foo8(e1: E1?, e2: E2, t: T) {
+    e1 == t
+    t == e1
+
+    e2 == t
+    t == e2
+
+    E1.A == t
+    t == E1.A
+}
+
+fun <T, K> foo9(e1: E1?, e2: E2, t: T, k: K) where T : MyInterface, T : MyOpenClass, K : MyInterface {
+    <!INCOMPATIBLE_ENUM_COMPARISON_ERROR!>e1 == t<!>
+    <!INCOMPATIBLE_ENUM_COMPARISON_ERROR!>t == e1<!>
+
+    <!INCOMPATIBLE_ENUM_COMPARISON_ERROR!>e2 == t<!>
+    <!INCOMPATIBLE_ENUM_COMPARISON_ERROR!>t == e2<!>
+
+    <!INCOMPATIBLE_ENUM_COMPARISON_ERROR!>E1.A == t<!>
+    <!INCOMPATIBLE_ENUM_COMPARISON_ERROR!>t == E1.A<!>
+
+    <!INCOMPATIBLE_ENUM_COMPARISON_ERROR!>E3.X == t<!>
+
+    E3.X == k
+    k == E3.X
+}
+
+interface Inv<T>
+
+enum class E4 : Inv<Int> { A }
+
+fun foo10(e4: E4, invString: Inv<String>) {
+    e4 == invString
+    invString == e4
+
+    E4.A == invString
+    invString == E4.A
+}
\ No newline at end of file
diff --git a/compiler/testData/diagnostics/tests/enum/incompatibleEnums_1_4.txt b/compiler/testData/diagnostics/tests/enum/incompatibleEnums_1_4.txt
new file mode 100644
index 00000000000..5e46d9fc2e5
--- /dev/null
+++ b/compiler/testData/diagnostics/tests/enum/incompatibleEnums_1_4.txt
@@ -0,0 +1,113 @@
+package
+
+public fun foo1(/*0*/ e1: E1, /*1*/ e2: E2): kotlin.Unit
+public fun foo10(/*0*/ e4: E4, /*1*/ invString: Inv<kotlin.String>): kotlin.Unit
+public fun foo2(/*0*/ e1: E1, /*1*/ e2: E2): kotlin.Unit
+public fun foo3(/*0*/ e1: kotlin.Enum<E1>, /*1*/ e2: kotlin.Enum<E2>, /*2*/ e: kotlin.Enum<*>): kotlin.Unit
+public fun foo4(/*0*/ e1: E1, /*1*/ i: MyInterface, /*2*/ c: MyOpenClass): kotlin.Unit
+public fun foo5(/*0*/ i: MyInterface, /*1*/ a: kotlin.Any): kotlin.Unit
+public fun foo6(/*0*/ e1: E1?, /*1*/ e2: E2): kotlin.Unit
+public fun foo7(/*0*/ e1: E1?, /*1*/ e2: E2?): kotlin.Unit
+public fun </*0*/ T> foo8(/*0*/ e1: E1?, /*1*/ e2: E2, /*2*/ t: T): kotlin.Unit
+public fun </*0*/ T : MyInterface, /*1*/ K : MyInterface> foo9(/*0*/ e1: E1?, /*1*/ e2: E2, /*2*/ t: T, /*3*/ k: K): kotlin.Unit where T : MyOpenClass
+
+public final enum class E1 : kotlin.Enum<E1> {
+    enum entry A
+
+    enum entry B
+
+    private constructor E1()
+    public final override /*1*/ /*fake_override*/ val name: kotlin.String
+    public final override /*1*/ /*fake_override*/ val ordinal: kotlin.Int
+    protected final override /*1*/ /*fake_override*/ fun clone(): kotlin.Any
+    public final override /*1*/ /*fake_override*/ fun compareTo(/*0*/ other: E1): kotlin.Int
+    public final override /*1*/ /*fake_override*/ fun equals(/*0*/ other: kotlin.Any?): kotlin.Boolean
+    protected/*protected and package*/ final override /*1*/ /*fake_override*/ /*isHiddenForResolutionEverywhereBesideSupercalls*/ fun finalize(): kotlin.Unit
+    public final override /*1*/ /*fake_override*/ /*isHiddenForResolutionEverywhereBesideSupercalls*/ fun getDeclaringClass(): java.lang.Class<E1!>!
+    public final override /*1*/ /*fake_override*/ fun hashCode(): kotlin.Int
+    public open override /*1*/ /*fake_override*/ fun toString(): kotlin.String
+
+    // Static members
+    public final /*synthesized*/ fun valueOf(/*0*/ value: kotlin.String): E1
+    public final /*synthesized*/ fun values(): kotlin.Array<E1>
+}
+
+public final enum class E2 : kotlin.Enum<E2> {
+    enum entry A
+
+    enum entry B
+
+    private constructor E2()
+    public final override /*1*/ /*fake_override*/ val name: kotlin.String
+    public final override /*1*/ /*fake_override*/ val ordinal: kotlin.Int
+    protected final override /*1*/ /*fake_override*/ fun clone(): kotlin.Any
+    public final override /*1*/ /*fake_override*/ fun compareTo(/*0*/ other: E2): kotlin.Int
+    public final override /*1*/ /*fake_override*/ fun equals(/*0*/ other: kotlin.Any?): kotlin.Boolean
+    protected/*protected and package*/ final override /*1*/ /*fake_override*/ /*isHiddenForResolutionEverywhereBesideSupercalls*/ fun finalize(): kotlin.Unit
+    public final override /*1*/ /*fake_override*/ /*isHiddenForResolutionEverywhereBesideSupercalls*/ fun getDeclaringClass(): java.lang.Class<E2!>!
+    public final override /*1*/ /*fake_override*/ fun hashCode(): kotlin.Int
+    public open override /*1*/ /*fake_override*/ fun toString(): kotlin.String
+
+    // Static members
+    public final /*synthesized*/ fun valueOf(/*0*/ value: kotlin.String): E2
+    public final /*synthesized*/ fun values(): kotlin.Array<E2>
+}
+
+public final enum class E3 : kotlin.Enum<E3>, MyInterface {
+    enum entry X
+
+    enum entry Y
+
+    private constructor E3()
+    public final override /*1*/ /*fake_override*/ val name: kotlin.String
+    public final override /*1*/ /*fake_override*/ val ordinal: kotlin.Int
+    protected final override /*1*/ /*fake_override*/ fun clone(): kotlin.Any
+    public final override /*1*/ /*fake_override*/ fun compareTo(/*0*/ other: E3): kotlin.Int
+    public final override /*2*/ /*fake_override*/ fun equals(/*0*/ other: kotlin.Any?): kotlin.Boolean
+    protected/*protected and package*/ final override /*1*/ /*fake_override*/ /*isHiddenForResolutionEverywhereBesideSupercalls*/ fun finalize(): kotlin.Unit
+    public final override /*1*/ /*fake_override*/ /*isHiddenForResolutionEverywhereBesideSupercalls*/ fun getDeclaringClass(): java.lang.Class<E3!>!
+    public final override /*2*/ /*fake_override*/ fun hashCode(): kotlin.Int
+    public open override /*2*/ /*fake_override*/ fun toString(): kotlin.String
+
+    // Static members
+    public final /*synthesized*/ fun valueOf(/*0*/ value: kotlin.String): E3
+    public final /*synthesized*/ fun values(): kotlin.Array<E3>
+}
+
+public final enum class E4 : kotlin.Enum<E4>, Inv<kotlin.Int> {
+    enum entry A
+
+    private constructor E4()
+    public final override /*1*/ /*fake_override*/ val name: kotlin.String
+    public final override /*1*/ /*fake_override*/ val ordinal: kotlin.Int
+    protected final override /*1*/ /*fake_override*/ fun clone(): kotlin.Any
+    public final override /*1*/ /*fake_override*/ fun compareTo(/*0*/ other: E4): kotlin.Int
+    public final override /*2*/ /*fake_override*/ fun equals(/*0*/ other: kotlin.Any?): kotlin.Boolean
+    protected/*protected and package*/ final override /*1*/ /*fake_override*/ /*isHiddenForResolutionEverywhereBesideSupercalls*/ fun finalize(): kotlin.Unit
+    public final override /*1*/ /*fake_override*/ /*isHiddenForResolutionEverywhereBesideSupercalls*/ fun getDeclaringClass(): java.lang.Class<E4!>!
+    public final override /*2*/ /*fake_override*/ fun hashCode(): kotlin.Int
+    public open override /*2*/ /*fake_override*/ fun toString(): kotlin.String
+
+    // Static members
+    public final /*synthesized*/ fun valueOf(/*0*/ value: kotlin.String): E4
+    public final /*synthesized*/ fun values(): kotlin.Array<E4>
+}
+
+public interface Inv</*0*/ T> {
+    public open override /*1*/ /*fake_override*/ fun equals(/*0*/ other: kotlin.Any?): kotlin.Boolean
+    public open override /*1*/ /*fake_override*/ fun hashCode(): kotlin.Int
+    public open override /*1*/ /*fake_override*/ fun toString(): kotlin.String
+}
+
+public interface MyInterface {
+    public open override /*1*/ /*fake_override*/ fun equals(/*0*/ other: kotlin.Any?): kotlin.Boolean
+    public open override /*1*/ /*fake_override*/ fun hashCode(): kotlin.Int
+    public open override /*1*/ /*fake_override*/ fun toString(): kotlin.String
+}
+
+public open class MyOpenClass {
+    public constructor MyOpenClass()
+    public open override /*1*/ /*fake_override*/ fun equals(/*0*/ other: kotlin.Any?): kotlin.Boolean
+    public open override /*1*/ /*fake_override*/ fun hashCode(): kotlin.Int
+    public open override /*1*/ /*fake_override*/ fun toString(): kotlin.String
+}
diff --git a/compiler/tests/org/jetbrains/kotlin/checkers/DiagnosticsTestGenerated.java b/compiler/tests/org/jetbrains/kotlin/checkers/DiagnosticsTestGenerated.java
index 98b7ccd5d6c..7aa173791f7 100644
--- a/compiler/tests/org/jetbrains/kotlin/checkers/DiagnosticsTestGenerated.java
+++ b/compiler/tests/org/jetbrains/kotlin/checkers/DiagnosticsTestGenerated.java
@@ -6943,6 +6943,11 @@ public class DiagnosticsTestGenerated extends AbstractDiagnosticsTest {
                 runTest("compiler/testData/diagnostics/tests/enum/incompatibleEnums.kt");
             }
 
+            @TestMetadata("incompatibleEnums_1_4.kt")
+            public void testIncompatibleEnums_1_4() throws Exception {
+                runTest("compiler/testData/diagnostics/tests/enum/incompatibleEnums_1_4.kt");
+            }
+
             @TestMetadata("inheritFromEnumEntry.kt")
             public void testInheritFromEnumEntry() throws Exception {
                 runTest("compiler/testData/diagnostics/tests/enum/inheritFromEnumEntry.kt");
diff --git a/compiler/tests/org/jetbrains/kotlin/checkers/javac/DiagnosticsUsingJavacTestGenerated.java b/compiler/tests/org/jetbrains/kotlin/checkers/javac/DiagnosticsUsingJavacTestGenerated.java
index 7d1c2d9e990..96e3b60f822 100644
--- a/compiler/tests/org/jetbrains/kotlin/checkers/javac/DiagnosticsUsingJavacTestGenerated.java
+++ b/compiler/tests/org/jetbrains/kotlin/checkers/javac/DiagnosticsUsingJavacTestGenerated.java
@@ -6938,6 +6938,11 @@ public class DiagnosticsUsingJavacTestGenerated extends AbstractDiagnosticsUsing
                 runTest("compiler/testData/diagnostics/tests/enum/incompatibleEnums.kt");
             }
 
+            @TestMetadata("incompatibleEnums_1_4.kt")
+            public void testIncompatibleEnums_1_4() throws Exception {
+                runTest("compiler/testData/diagnostics/tests/enum/incompatibleEnums_1_4.kt");
+            }
+
             @TestMetadata("inheritFromEnumEntry.kt")
             public void testInheritFromEnumEntry() throws Exception {
                 runTest("compiler/testData/diagnostics/tests/enum/inheritFromEnumEntry.kt");
diff --git a/compiler/util/src/org/jetbrains/kotlin/config/LanguageVersionSettings.kt b/compiler/util/src/org/jetbrains/kotlin/config/LanguageVersionSettings.kt
index e9b077bd465..d9da258ca42 100644
--- a/compiler/util/src/org/jetbrains/kotlin/config/LanguageVersionSettings.kt
+++ b/compiler/util/src/org/jetbrains/kotlin/config/LanguageVersionSettings.kt
@@ -101,6 +101,7 @@ enum class LanguageFeature(
     ProhibitRepeatedUseSiteTargetAnnotations(KOTLIN_1_4, kind = BUG_FIX),
     ProhibitUseSiteTargetAnnotationsOnSuperTypes(KOTLIN_1_4, kind = BUG_FIX),
     ProhibitTypeParametersInClassLiteralsInAnnotationArguments(KOTLIN_1_4, kind = BUG_FIX),
+    ProhibitComparisonOfIncompatibleEnums(KOTLIN_1_4, kind = BUG_FIX),
 
     ProperVisibilityForCompanionObjectInstanceField(sinceVersion = null, kind = BUG_FIX),
     // Temporarily disabled, see KT-27084/KT-22379
diff --git a/core/descriptors/src/org/jetbrains/kotlin/types/TypeUtils.kt b/core/descriptors/src/org/jetbrains/kotlin/types/TypeUtils.kt
index ac900d95a39..6a648da508e 100644
--- a/core/descriptors/src/org/jetbrains/kotlin/types/TypeUtils.kt
+++ b/core/descriptors/src/org/jetbrains/kotlin/types/TypeUtils.kt
@@ -54,6 +54,7 @@ fun KotlinType.supertypes(): Collection<KotlinType> = TypeUtils.getAllSupertypes
 
 fun KotlinType.isNothing(): Boolean = KotlinBuiltIns.isNothing(this)
 fun KotlinType.isNullableNothing(): Boolean = KotlinBuiltIns.isNullableNothing(this)
+fun KotlinType.isNothingOrNullableNothing(): Boolean = KotlinBuiltIns.isNothingOrNullableNothing(this)
 fun KotlinType.isUnit(): Boolean = KotlinBuiltIns.isUnit(this)
 fun KotlinType.isAnyOrNullableAny(): Boolean = KotlinBuiltIns.isAnyOrNullableAny(this)
 fun KotlinType.isNullableAny(): Boolean = KotlinBuiltIns.isNullableAny(this)