diff --git a/compiler/fir/analysis-tests/testData/resolve/diagnostics/conflictingProjection.kt b/compiler/fir/analysis-tests/testData/resolve/diagnostics/conflictingProjection.kt
new file mode 100644
index 00000000000..2e46ea04ee0
--- /dev/null
+++ b/compiler/fir/analysis-tests/testData/resolve/diagnostics/conflictingProjection.kt
@@ -0,0 +1,95 @@
+class None<T>
+class In<in T>
+class Out<out T>
+
+fun a1(value: None<Int>) {}
+fun a2(value: None<in Int>) {}
+fun a3(value: None<out Int>) {}
+
+fun a4(value: In<Int>) {}
+fun a5(value: In<in Int>) {}
+fun a6(value: <!CONFLICTING_PROJECTION!>In<out Int><!>) {}
+
+fun a7(value: Out<Int>) {}
+fun a8(value: <!CONFLICTING_PROJECTION!>Out<in Int><!>) {}
+fun a9(value: Out<out Int>) {}
+
+typealias A1<K> = None<K>
+typealias A2<K> = None<in K>
+typealias A3<K> = None<out K>
+
+typealias A4<<!VARIANCE_ON_TYPE_PARAMETER_NOT_ALLOWED!>in K<!>> = None<K>
+typealias A5<<!VARIANCE_ON_TYPE_PARAMETER_NOT_ALLOWED!>in K<!>> = None<in K>
+typealias A6<<!VARIANCE_ON_TYPE_PARAMETER_NOT_ALLOWED!>in K<!>> = None<out K>
+
+typealias A7<<!VARIANCE_ON_TYPE_PARAMETER_NOT_ALLOWED!>out K<!>> = None<K>
+typealias A8<<!VARIANCE_ON_TYPE_PARAMETER_NOT_ALLOWED!>out K<!>> = None<in K>
+typealias A9<<!VARIANCE_ON_TYPE_PARAMETER_NOT_ALLOWED!>out K<!>> = None<out K>
+
+typealias A10<K> = In<K>
+typealias A11<K> = In<in K>
+typealias A12<K> = <!CONFLICTING_PROJECTION!>In<out K><!>
+
+typealias A13<<!VARIANCE_ON_TYPE_PARAMETER_NOT_ALLOWED!>in K<!>> = In<K>
+typealias A14<<!VARIANCE_ON_TYPE_PARAMETER_NOT_ALLOWED!>in K<!>> = In<in K>
+typealias A15<<!VARIANCE_ON_TYPE_PARAMETER_NOT_ALLOWED!>in K<!>> = <!CONFLICTING_PROJECTION!>In<out K><!>
+
+typealias A16<<!VARIANCE_ON_TYPE_PARAMETER_NOT_ALLOWED!>out K<!>> = In<K>
+typealias A17<<!VARIANCE_ON_TYPE_PARAMETER_NOT_ALLOWED!>out K<!>> = In<in K>
+typealias A18<<!VARIANCE_ON_TYPE_PARAMETER_NOT_ALLOWED!>out K<!>> = <!CONFLICTING_PROJECTION!>In<out K><!>
+
+typealias A19<K> = Out<K>
+typealias A20<K> = <!CONFLICTING_PROJECTION!>Out<in K><!>
+typealias A21<K> = Out<out K>
+
+typealias A22<<!VARIANCE_ON_TYPE_PARAMETER_NOT_ALLOWED!>in K<!>> = Out<K>
+typealias A23<<!VARIANCE_ON_TYPE_PARAMETER_NOT_ALLOWED!>in K<!>> = <!CONFLICTING_PROJECTION!>Out<in K><!>
+typealias A24<<!VARIANCE_ON_TYPE_PARAMETER_NOT_ALLOWED!>in K<!>> = Out<out K>
+
+typealias A25<<!VARIANCE_ON_TYPE_PARAMETER_NOT_ALLOWED!>out K<!>> = Out<K>
+typealias A26<<!VARIANCE_ON_TYPE_PARAMETER_NOT_ALLOWED!>out K<!>> = <!CONFLICTING_PROJECTION!>Out<in K><!>
+typealias A27<<!VARIANCE_ON_TYPE_PARAMETER_NOT_ALLOWED!>out K<!>> = Out<out K>
+
+class Outer<T> {
+    inner class Intermediate<K> {
+        inner class Inner<G> {
+
+        }
+    }
+}
+
+fun test1(): Outer<Int>.Intermediate<String>.Inner<Char> = Outer<Int>().Intermediate<String>().Inner()
+
+fun test2(): Outer<in Int>.Intermediate<String>.Inner<Char> = Outer<Int>().Intermediate<String>().Inner()
+fun test3(): Outer<out Int>.Intermediate<String>.Inner<Char> = Outer<Int>().Intermediate<String>().Inner()
+
+fun test4(): Outer<Int>.Intermediate<in String>.Inner<Char> = Outer<Int>().Intermediate<String>().Inner()
+fun test5(): Outer<Int>.Intermediate<out String>.Inner<Char> = Outer<Int>().Intermediate<String>().Inner()
+
+fun test6(): Outer<Int>.Intermediate<String>.Inner<in Char> = Outer<Int>().Intermediate<String>().Inner()
+fun test7(): Outer<Int>.Intermediate<String>.Inner<out Char> = Outer<Int>().Intermediate<String>().Inner()
+
+fun test8(): Outer<in Int>.Intermediate<out String>.Inner<Char> = Outer<Int>().Intermediate<String>().Inner()
+fun test9(): Outer<Int>.Intermediate<in String>.Inner<out Char> = Outer<Int>().Intermediate<String>().Inner()
+
+class InOuter<in T> {
+    inner class OutIntermediate<out K> {
+        inner class InInner<in G> {
+
+        }
+    }
+}
+
+fun test10(): InOuter<Int>.OutIntermediate<String>.InInner<Char> = InOuter<Int>().OutIntermediate<String>().InInner()
+
+fun test11(): InOuter<in Int>.OutIntermediate<String>.InInner<Char> = InOuter<Int>().OutIntermediate<String>().InInner()
+fun test12(): <!CONFLICTING_PROJECTION!>InOuter<out Int>.OutIntermediate<String>.InInner<Char><!> = InOuter<Int>().OutIntermediate<String>().InInner()
+
+fun test13(): <!CONFLICTING_PROJECTION!>InOuter<Int>.OutIntermediate<in String>.InInner<Char><!> = InOuter<Int>().OutIntermediate<String>().InInner()
+fun test14(): InOuter<Int>.OutIntermediate<out String>.InInner<Char> = InOuter<Int>().OutIntermediate<String>().InInner()
+
+fun test15(): InOuter<Int>.OutIntermediate<String>.InInner<in Char> = InOuter<Int>().OutIntermediate<String>().InInner()
+fun test16(): <!CONFLICTING_PROJECTION!>InOuter<Int>.OutIntermediate<String>.InInner<out Char><!> = InOuter<Int>().OutIntermediate<String>().InInner()
+
+fun test17(): InOuter<in Int>.OutIntermediate<out String>.InInner<Char> = InOuter<Int>().OutIntermediate<String>().InInner()
+fun test18(): <!CONFLICTING_PROJECTION!>InOuter<Int>.OutIntermediate<in String>.InInner<out Char><!> = InOuter<Int>().OutIntermediate<String>().InInner()
diff --git a/compiler/fir/analysis-tests/testData/resolve/diagnostics/conflictingProjection.txt b/compiler/fir/analysis-tests/testData/resolve/diagnostics/conflictingProjection.txt
new file mode 100644
index 00000000000..8c5f49a4850
--- /dev/null
+++ b/compiler/fir/analysis-tests/testData/resolve/diagnostics/conflictingProjection.txt
@@ -0,0 +1,158 @@
+FILE: conflictingProjection.kt
+    public final class None<T> : R|kotlin/Any| {
+        public constructor<T>(): R|None<T>| {
+            super<R|kotlin/Any|>()
+        }
+
+    }
+    public final class In<in T> : R|kotlin/Any| {
+        public constructor<in T>(): R|In<T>| {
+            super<R|kotlin/Any|>()
+        }
+
+    }
+    public final class Out<out T> : R|kotlin/Any| {
+        public constructor<out T>(): R|Out<T>| {
+            super<R|kotlin/Any|>()
+        }
+
+    }
+    public final fun a1(value: R|None<kotlin/Int>|): R|kotlin/Unit| {
+    }
+    public final fun a2(value: R|None<in kotlin/Int>|): R|kotlin/Unit| {
+    }
+    public final fun a3(value: R|None<out kotlin/Int>|): R|kotlin/Unit| {
+    }
+    public final fun a4(value: R|In<kotlin/Int>|): R|kotlin/Unit| {
+    }
+    public final fun a5(value: R|In<in kotlin/Int>|): R|kotlin/Unit| {
+    }
+    public final fun a6(value: R|In<out kotlin/Int>|): R|kotlin/Unit| {
+    }
+    public final fun a7(value: R|Out<kotlin/Int>|): R|kotlin/Unit| {
+    }
+    public final fun a8(value: R|Out<in kotlin/Int>|): R|kotlin/Unit| {
+    }
+    public final fun a9(value: R|Out<out kotlin/Int>|): R|kotlin/Unit| {
+    }
+    public final typealias A1<K> = R|None<K>|
+    public final typealias A2<K> = R|None<in K>|
+    public final typealias A3<K> = R|None<out K>|
+    public final typealias A4<in K> = R|None<K>|
+    public final typealias A5<in K> = R|None<in K>|
+    public final typealias A6<in K> = R|None<out K>|
+    public final typealias A7<out K> = R|None<K>|
+    public final typealias A8<out K> = R|None<in K>|
+    public final typealias A9<out K> = R|None<out K>|
+    public final typealias A10<K> = R|In<K>|
+    public final typealias A11<K> = R|In<in K>|
+    public final typealias A12<K> = R|In<out K>|
+    public final typealias A13<in K> = R|In<K>|
+    public final typealias A14<in K> = R|In<in K>|
+    public final typealias A15<in K> = R|In<out K>|
+    public final typealias A16<out K> = R|In<K>|
+    public final typealias A17<out K> = R|In<in K>|
+    public final typealias A18<out K> = R|In<out K>|
+    public final typealias A19<K> = R|Out<K>|
+    public final typealias A20<K> = R|Out<in K>|
+    public final typealias A21<K> = R|Out<out K>|
+    public final typealias A22<in K> = R|Out<K>|
+    public final typealias A23<in K> = R|Out<in K>|
+    public final typealias A24<in K> = R|Out<out K>|
+    public final typealias A25<out K> = R|Out<K>|
+    public final typealias A26<out K> = R|Out<in K>|
+    public final typealias A27<out K> = R|Out<out K>|
+    public final class Outer<T> : R|kotlin/Any| {
+        public constructor<T>(): R|Outer<T>| {
+            super<R|kotlin/Any|>()
+        }
+
+        public final inner class Intermediate<K, T> : R|kotlin/Any| {
+            public constructor<K>(): R|Outer.Intermediate<K, T>| {
+                super<R|kotlin/Any|>()
+            }
+
+            public final inner class Inner<G, K, T> : R|kotlin/Any| {
+                public constructor<G>(): R|Outer.Intermediate.Inner<G, K, T>| {
+                    super<R|kotlin/Any|>()
+                }
+
+            }
+
+        }
+
+    }
+    public final fun test1(): R|Outer.Intermediate.Inner<kotlin/Char, kotlin/String, kotlin/Int>| {
+        ^test1 R|/Outer.Outer|<R|kotlin/Int|>().R|/Outer.Intermediate.Intermediate|<R|kotlin/String|>().R|/Outer.Intermediate.Inner.Inner|<R|kotlin/Char|>()
+    }
+    public final fun test2(): R|Outer.Intermediate.Inner<kotlin/Char, kotlin/String, in kotlin/Int>| {
+        ^test2 R|/Outer.Outer|<R|kotlin/Int|>().R|/Outer.Intermediate.Intermediate|<R|kotlin/String|>().R|/Outer.Intermediate.Inner.Inner|<R|kotlin/Char|>()
+    }
+    public final fun test3(): R|Outer.Intermediate.Inner<kotlin/Char, kotlin/String, out kotlin/Int>| {
+        ^test3 R|/Outer.Outer|<R|kotlin/Int|>().R|/Outer.Intermediate.Intermediate|<R|kotlin/String|>().R|/Outer.Intermediate.Inner.Inner|<R|kotlin/Char|>()
+    }
+    public final fun test4(): R|Outer.Intermediate.Inner<kotlin/Char, in kotlin/String, kotlin/Int>| {
+        ^test4 R|/Outer.Outer|<R|kotlin/Int|>().R|/Outer.Intermediate.Intermediate|<R|kotlin/String|>().R|/Outer.Intermediate.Inner.Inner|<R|kotlin/Char|>()
+    }
+    public final fun test5(): R|Outer.Intermediate.Inner<kotlin/Char, out kotlin/String, kotlin/Int>| {
+        ^test5 R|/Outer.Outer|<R|kotlin/Int|>().R|/Outer.Intermediate.Intermediate|<R|kotlin/String|>().R|/Outer.Intermediate.Inner.Inner|<R|kotlin/Char|>()
+    }
+    public final fun test6(): R|Outer.Intermediate.Inner<in kotlin/Char, kotlin/String, kotlin/Int>| {
+        ^test6 R|/Outer.Outer|<R|kotlin/Int|>().R|/Outer.Intermediate.Intermediate|<R|kotlin/String|>().R|/Outer.Intermediate.Inner.Inner|<R|kotlin/Char|>()
+    }
+    public final fun test7(): R|Outer.Intermediate.Inner<out kotlin/Char, kotlin/String, kotlin/Int>| {
+        ^test7 R|/Outer.Outer|<R|kotlin/Int|>().R|/Outer.Intermediate.Intermediate|<R|kotlin/String|>().R|/Outer.Intermediate.Inner.Inner|<R|kotlin/Char|>()
+    }
+    public final fun test8(): R|Outer.Intermediate.Inner<kotlin/Char, out kotlin/String, in kotlin/Int>| {
+        ^test8 R|/Outer.Outer|<R|kotlin/Int|>().R|/Outer.Intermediate.Intermediate|<R|kotlin/String|>().R|/Outer.Intermediate.Inner.Inner|<R|kotlin/Char|>()
+    }
+    public final fun test9(): R|Outer.Intermediate.Inner<out kotlin/Char, in kotlin/String, kotlin/Int>| {
+        ^test9 R|/Outer.Outer|<R|kotlin/Int|>().R|/Outer.Intermediate.Intermediate|<R|kotlin/String|>().R|/Outer.Intermediate.Inner.Inner|<R|kotlin/Char|>()
+    }
+    public final class InOuter<in T> : R|kotlin/Any| {
+        public constructor<in T>(): R|InOuter<T>| {
+            super<R|kotlin/Any|>()
+        }
+
+        public final inner class OutIntermediate<out K, in T> : R|kotlin/Any| {
+            public constructor<out K>(): R|InOuter.OutIntermediate<K, T>| {
+                super<R|kotlin/Any|>()
+            }
+
+            public final inner class InInner<in G, out K, in T> : R|kotlin/Any| {
+                public constructor<in G>(): R|InOuter.OutIntermediate.InInner<G, K, T>| {
+                    super<R|kotlin/Any|>()
+                }
+
+            }
+
+        }
+
+    }
+    public final fun test10(): R|InOuter.OutIntermediate.InInner<kotlin/Char, kotlin/String, kotlin/Int>| {
+        ^test10 R|/InOuter.InOuter|<R|kotlin/Int|>().R|/InOuter.OutIntermediate.OutIntermediate|<R|kotlin/String|>().R|/InOuter.OutIntermediate.InInner.InInner|<R|kotlin/Char|>()
+    }
+    public final fun test11(): R|InOuter.OutIntermediate.InInner<kotlin/Char, kotlin/String, in kotlin/Int>| {
+        ^test11 R|/InOuter.InOuter|<R|kotlin/Int|>().R|/InOuter.OutIntermediate.OutIntermediate|<R|kotlin/String|>().R|/InOuter.OutIntermediate.InInner.InInner|<R|kotlin/Char|>()
+    }
+    public final fun test12(): R|InOuter.OutIntermediate.InInner<kotlin/Char, kotlin/String, out kotlin/Int>| {
+        ^test12 R|/InOuter.InOuter|<R|kotlin/Int|>().R|/InOuter.OutIntermediate.OutIntermediate|<R|kotlin/String|>().R|/InOuter.OutIntermediate.InInner.InInner|<R|kotlin/Char|>()
+    }
+    public final fun test13(): R|InOuter.OutIntermediate.InInner<kotlin/Char, in kotlin/String, kotlin/Int>| {
+        ^test13 R|/InOuter.InOuter|<R|kotlin/Int|>().R|/InOuter.OutIntermediate.OutIntermediate|<R|kotlin/String|>().R|/InOuter.OutIntermediate.InInner.InInner|<R|kotlin/Char|>()
+    }
+    public final fun test14(): R|InOuter.OutIntermediate.InInner<kotlin/Char, out kotlin/String, kotlin/Int>| {
+        ^test14 R|/InOuter.InOuter|<R|kotlin/Int|>().R|/InOuter.OutIntermediate.OutIntermediate|<R|kotlin/String|>().R|/InOuter.OutIntermediate.InInner.InInner|<R|kotlin/Char|>()
+    }
+    public final fun test15(): R|InOuter.OutIntermediate.InInner<in kotlin/Char, kotlin/String, kotlin/Int>| {
+        ^test15 R|/InOuter.InOuter|<R|kotlin/Int|>().R|/InOuter.OutIntermediate.OutIntermediate|<R|kotlin/String|>().R|/InOuter.OutIntermediate.InInner.InInner|<R|kotlin/Char|>()
+    }
+    public final fun test16(): R|InOuter.OutIntermediate.InInner<out kotlin/Char, kotlin/String, kotlin/Int>| {
+        ^test16 R|/InOuter.InOuter|<R|kotlin/Int|>().R|/InOuter.OutIntermediate.OutIntermediate|<R|kotlin/String|>().R|/InOuter.OutIntermediate.InInner.InInner|<R|kotlin/Any?|>()
+    }
+    public final fun test17(): R|InOuter.OutIntermediate.InInner<kotlin/Char, out kotlin/String, in kotlin/Int>| {
+        ^test17 R|/InOuter.InOuter|<R|kotlin/Int|>().R|/InOuter.OutIntermediate.OutIntermediate|<R|kotlin/String|>().R|/InOuter.OutIntermediate.InInner.InInner|<R|kotlin/Char|>()
+    }
+    public final fun test18(): R|InOuter.OutIntermediate.InInner<out kotlin/Char, in kotlin/String, kotlin/Int>| {
+        ^test18 R|/InOuter.InOuter|<R|kotlin/Int|>().R|/InOuter.OutIntermediate.OutIntermediate|<R|kotlin/String|>().R|/InOuter.OutIntermediate.InInner.InInner|<R|kotlin/Any?|>()
+    }
diff --git a/compiler/fir/analysis-tests/tests/org/jetbrains/kotlin/fir/FirDiagnosticsTestGenerated.java b/compiler/fir/analysis-tests/tests/org/jetbrains/kotlin/fir/FirDiagnosticsTestGenerated.java
index e6f6db5e04a..a7e9be1e2a5 100644
--- a/compiler/fir/analysis-tests/tests/org/jetbrains/kotlin/fir/FirDiagnosticsTestGenerated.java
+++ b/compiler/fir/analysis-tests/tests/org/jetbrains/kotlin/fir/FirDiagnosticsTestGenerated.java
@@ -931,6 +931,11 @@ public class FirDiagnosticsTestGenerated extends AbstractFirDiagnosticsTest {
             runTest("compiler/fir/analysis-tests/testData/resolve/diagnostics/conflictingOverloads.kt");
         }
 
+        @TestMetadata("conflictingProjection.kt")
+        public void testConflictingProjection() throws Exception {
+            runTest("compiler/fir/analysis-tests/testData/resolve/diagnostics/conflictingProjection.kt");
+        }
+
         @TestMetadata("constructorInInterface.kt")
         public void testConstructorInInterface() throws Exception {
             runTest("compiler/fir/analysis-tests/testData/resolve/diagnostics/constructorInInterface.kt");
diff --git a/compiler/fir/analysis-tests/tests/org/jetbrains/kotlin/fir/FirDiagnosticsWithLightTreeTestGenerated.java b/compiler/fir/analysis-tests/tests/org/jetbrains/kotlin/fir/FirDiagnosticsWithLightTreeTestGenerated.java
index 456baab903f..c389ebf3906 100644
--- a/compiler/fir/analysis-tests/tests/org/jetbrains/kotlin/fir/FirDiagnosticsWithLightTreeTestGenerated.java
+++ b/compiler/fir/analysis-tests/tests/org/jetbrains/kotlin/fir/FirDiagnosticsWithLightTreeTestGenerated.java
@@ -931,6 +931,11 @@ public class FirDiagnosticsWithLightTreeTestGenerated extends AbstractFirDiagnos
             runTest("compiler/fir/analysis-tests/testData/resolve/diagnostics/conflictingOverloads.kt");
         }
 
+        @TestMetadata("conflictingProjection.kt")
+        public void testConflictingProjection() throws Exception {
+            runTest("compiler/fir/analysis-tests/testData/resolve/diagnostics/conflictingProjection.kt");
+        }
+
         @TestMetadata("constructorInInterface.kt")
         public void testConstructorInInterface() throws Exception {
             runTest("compiler/fir/analysis-tests/testData/resolve/diagnostics/constructorInInterface.kt");
diff --git a/compiler/fir/checkers/src/org/jetbrains/kotlin/fir/analysis/checkers/declaration/DefaultDeclarationCheckers.kt b/compiler/fir/checkers/src/org/jetbrains/kotlin/fir/analysis/checkers/declaration/DefaultDeclarationCheckers.kt
index d45d148d4ae..b98fddb6e36 100644
--- a/compiler/fir/checkers/src/org/jetbrains/kotlin/fir/analysis/checkers/declaration/DefaultDeclarationCheckers.kt
+++ b/compiler/fir/checkers/src/org/jetbrains/kotlin/fir/analysis/checkers/declaration/DefaultDeclarationCheckers.kt
@@ -23,6 +23,7 @@ object CommonDeclarationCheckers : DeclarationCheckers() {
         FirTypeParametersInObjectChecker,
         FirConflictsChecker,
         FirConstructorInInterfaceChecker,
+        FirConflictingProjectionChecker,
     )
 
     override val memberDeclarationCheckers: List<FirMemberDeclarationChecker> = listOf(
diff --git a/compiler/fir/checkers/src/org/jetbrains/kotlin/fir/analysis/checkers/declaration/FirConflictingProjectionChecker.kt b/compiler/fir/checkers/src/org/jetbrains/kotlin/fir/analysis/checkers/declaration/FirConflictingProjectionChecker.kt
new file mode 100644
index 00000000000..f0c438e2c91
--- /dev/null
+++ b/compiler/fir/checkers/src/org/jetbrains/kotlin/fir/analysis/checkers/declaration/FirConflictingProjectionChecker.kt
@@ -0,0 +1,86 @@
+/*
+ * Copyright 2010-2020 JetBrains s.r.o. and Kotlin Programming Language contributors.
+ * 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.fir.analysis.checkers.declaration
+
+import org.jetbrains.kotlin.fir.FirSourceElement
+import org.jetbrains.kotlin.fir.analysis.checkers.context.CheckerContext
+import org.jetbrains.kotlin.fir.analysis.diagnostics.DiagnosticReporter
+import org.jetbrains.kotlin.fir.analysis.diagnostics.FirErrors
+import org.jetbrains.kotlin.fir.declarations.*
+import org.jetbrains.kotlin.fir.resolve.toSymbol
+import org.jetbrains.kotlin.fir.types.*
+import org.jetbrains.kotlin.types.Variance
+import org.jetbrains.kotlin.utils.addToStdlib.safeAs
+
+object FirConflictingProjectionChecker : FirBasicDeclarationChecker() {
+    override fun check(declaration: FirDeclaration, context: CheckerContext, reporter: DiagnosticReporter) {
+        // we can't just check for FirTypedDeclaration
+        // because it leads to duplicate reports for
+        // some cases. Maybe we should fix this via not
+        // visiting the same firs twice instead.
+        when (declaration) {
+            is FirPropertyAccessor -> {}
+            is FirProperty -> {
+                checkTypeRef(declaration.returnTypeRef, context, reporter)
+            }
+            is FirFunction<*> -> {
+                for (it in declaration.valueParameters) {
+                    checkTypeRef(it.returnTypeRef, context, reporter)
+                }
+                checkTypeRef(declaration.returnTypeRef, context, reporter)
+            }
+            is FirClass<*> -> {
+                for (it in declaration.superTypeRefs) {
+                    checkTypeRef(it, context, reporter)
+                }
+            }
+            is FirTypeAlias -> {
+                for (it in declaration.typeParameters) {
+                    if (it.variance != Variance.INVARIANT) {
+                        reporter.reportVarianceNotAllowed(it.source)
+                    }
+                }
+                checkTypeRef(declaration.expandedTypeRef, context, reporter)
+            }
+        }
+    }
+
+    private fun checkTypeRef(typeRef: FirTypeRef, context: CheckerContext, reporter: DiagnosticReporter) {
+        val declaration = typeRef.safeAs<FirResolvedTypeRef>()
+            ?.coneTypeSafe<ConeClassLikeType>()
+            ?.lookupTag
+            ?.toSymbol(context.session)
+            ?.fir.safeAs<FirRegularClass>()
+            ?: return
+
+        declaration.typeParameters.zip(typeRef.coneType.typeArguments).forEach { (proto, actual) ->
+            val protoVariance = proto.safeAs<FirTypeParameterRef>()
+                ?.symbol?.fir
+                ?.variance
+                ?: return@forEach
+
+            if (protoVariance == Variance.INVARIANT) {
+                return@forEach
+            }
+
+            if (
+                actual is ConeKotlinTypeProjectionIn && protoVariance == Variance.OUT_VARIANCE ||
+                actual is ConeKotlinTypeProjectionOut && protoVariance == Variance.IN_VARIANCE
+            ) {
+                reporter.reportConflictingProjections(typeRef.source, typeRef.coneType.toString())
+                return
+            }
+        }
+    }
+
+    private fun DiagnosticReporter.reportConflictingProjections(source: FirSourceElement?, desiredProjection: String) {
+        source?.let { report(FirErrors.CONFLICTING_PROJECTION.on(it, desiredProjection)) }
+    }
+
+    private fun DiagnosticReporter.reportVarianceNotAllowed(source: FirSourceElement?) {
+        source?.let { report(FirErrors.VARIANCE_ON_TYPE_PARAMETER_NOT_ALLOWED.on(it)) }
+    }
+}
\ No newline at end of file
diff --git a/compiler/fir/checkers/src/org/jetbrains/kotlin/fir/analysis/diagnostics/FirDefaultErrorMessages.kt b/compiler/fir/checkers/src/org/jetbrains/kotlin/fir/analysis/diagnostics/FirDefaultErrorMessages.kt
index f65fe522952..d1b280b5e5d 100644
--- a/compiler/fir/checkers/src/org/jetbrains/kotlin/fir/analysis/diagnostics/FirDefaultErrorMessages.kt
+++ b/compiler/fir/checkers/src/org/jetbrains/kotlin/fir/analysis/diagnostics/FirDefaultErrorMessages.kt
@@ -25,6 +25,7 @@ import org.jetbrains.kotlin.fir.analysis.diagnostics.FirErrors.CLASS_IN_SUPERTYP
 import org.jetbrains.kotlin.fir.analysis.diagnostics.FirErrors.CONFLICTING_OVERLOADS
 import org.jetbrains.kotlin.fir.analysis.diagnostics.FirErrors.CAN_BE_REPLACED_WITH_OPERATOR_ASSIGNMENT
 import org.jetbrains.kotlin.fir.analysis.diagnostics.FirErrors.CAN_BE_VAL
+import org.jetbrains.kotlin.fir.analysis.diagnostics.FirErrors.CONFLICTING_PROJECTION
 import org.jetbrains.kotlin.fir.analysis.diagnostics.FirErrors.CONSTRUCTOR_IN_INTERFACE
 import org.jetbrains.kotlin.fir.analysis.diagnostics.FirErrors.CONSTRUCTOR_IN_OBJECT
 import org.jetbrains.kotlin.fir.analysis.diagnostics.FirErrors.CYCLIC_CONSTRUCTOR_DELEGATION_CALL
@@ -104,6 +105,7 @@ import org.jetbrains.kotlin.fir.analysis.diagnostics.FirErrors.UNRESOLVED_LABEL
 import org.jetbrains.kotlin.fir.analysis.diagnostics.FirErrors.UNRESOLVED_REFERENCE
 import org.jetbrains.kotlin.fir.analysis.diagnostics.FirErrors.UPPER_BOUND_VIOLATED
 import org.jetbrains.kotlin.fir.analysis.diagnostics.FirErrors.VARIABLE_EXPECTED
+import org.jetbrains.kotlin.fir.analysis.diagnostics.FirErrors.VARIANCE_ON_TYPE_PARAMETER_NOT_ALLOWED
 import org.jetbrains.kotlin.fir.analysis.diagnostics.FirErrors.VAR_ANNOTATION_PARAMETER
 import org.jetbrains.kotlin.fir.analysis.diagnostics.FirErrors.WRONG_INVOCATION_KIND
 import org.jetbrains.kotlin.fir.analysis.diagnostics.FirErrors.WRONG_NUMBER_OF_TYPE_ARGUMENTS
@@ -254,6 +256,15 @@ class FirDefaultErrorMessages : DefaultErrorMessages.Extension {
             map.put(TYPE_PARAMETERS_IN_OBJECT, "Type parameters are not allowed for objects")
 //            map.put(ILLEGAL_PROJECTION_USAGE, ...) // &
             map.put(TYPE_PARAMETERS_IN_ENUM, "Enum class cannot have type parameters")
+            map.put(
+                CONFLICTING_PROJECTION,
+                "Projection is conflicting with variance of the corresponding type parameter of {0}. Remove the projection or replace it with ''*''",
+                TO_STRING
+            )
+            map.put(
+                VARIANCE_ON_TYPE_PARAMETER_NOT_ALLOWED,
+                "Variance annotations are only allowed for type parameters of classes and interfaces"
+            )
 
             // Redeclarations
             map.put(MANY_COMPANION_OBJECTS, "Only one companion object is allowed per class")
diff --git a/compiler/fir/checkers/src/org/jetbrains/kotlin/fir/analysis/diagnostics/FirErrors.kt b/compiler/fir/checkers/src/org/jetbrains/kotlin/fir/analysis/diagnostics/FirErrors.kt
index 865678217bb..557a52420e5 100644
--- a/compiler/fir/checkers/src/org/jetbrains/kotlin/fir/analysis/diagnostics/FirErrors.kt
+++ b/compiler/fir/checkers/src/org/jetbrains/kotlin/fir/analysis/diagnostics/FirErrors.kt
@@ -125,6 +125,8 @@ object FirErrors {
     val TYPE_PARAMETERS_IN_OBJECT by error0<FirSourceElement, PsiElement>()
     val ILLEGAL_PROJECTION_USAGE by error0<FirSourceElement, PsiElement>()
     val TYPE_PARAMETERS_IN_ENUM by error0<FirSourceElement, PsiElement>()
+    val CONFLICTING_PROJECTION by error1<FirSourceElement, PsiElement, String>()
+    val VARIANCE_ON_TYPE_PARAMETER_NOT_ALLOWED by error0<FirSourceElement, PsiElement>()
 
     // Redeclarations
     val MANY_COMPANION_OBJECTS by error0<FirSourceElement, PsiElement>()
diff --git a/compiler/testData/cli/jvm/conflictingProjection.args b/compiler/testData/cli/jvm/conflictingProjection.args
new file mode 100644
index 00000000000..3736b3db902
--- /dev/null
+++ b/compiler/testData/cli/jvm/conflictingProjection.args
@@ -0,0 +1,4 @@
+$TESTDATA_DIR$/conflictingProjection.kt
+-Xuse-fir
+-d
+$TEMP_DIR$
diff --git a/compiler/testData/cli/jvm/conflictingProjection.kt b/compiler/testData/cli/jvm/conflictingProjection.kt
new file mode 100644
index 00000000000..cd840208cef
--- /dev/null
+++ b/compiler/testData/cli/jvm/conflictingProjection.kt
@@ -0,0 +1,19 @@
+class None<T>
+class In<in T>
+class Out<out T>
+
+fun a1(value: None<Int>) {}
+fun a2(value: None<in Int>) {}
+fun a3(value: None<out Int>) {}
+
+fun a7(value: Out<Int>) {}
+fun a8(value: Out<in Int>) {}
+fun a9(value: Out<out Int>) {}
+
+typealias A1<K> = None<K>
+typealias A2<K> = None<in K>
+typealias A3<K> = None<out K>
+
+typealias A13<in K> = In<K>
+typealias A14<in K> = In<in K>
+typealias A15<in K> = In<out K>
diff --git a/compiler/testData/cli/jvm/conflictingProjection.out b/compiler/testData/cli/jvm/conflictingProjection.out
new file mode 100644
index 00000000000..3b8f7cc4d34
--- /dev/null
+++ b/compiler/testData/cli/jvm/conflictingProjection.out
@@ -0,0 +1,16 @@
+compiler/testData/cli/jvm/conflictingProjection.kt:10:15: error: projection is conflicting with variance of the corresponding type parameter of Out<in kotlin/Int>. Remove the projection or replace it with '*'
+fun a8(value: Out<in Int>) {}
+              ^
+compiler/testData/cli/jvm/conflictingProjection.kt:17:15: error: variance annotations are only allowed for type parameters of classes and interfaces
+typealias A13<in K> = In<K>
+              ^
+compiler/testData/cli/jvm/conflictingProjection.kt:18:15: error: variance annotations are only allowed for type parameters of classes and interfaces
+typealias A14<in K> = In<in K>
+              ^
+compiler/testData/cli/jvm/conflictingProjection.kt:19:15: error: variance annotations are only allowed for type parameters of classes and interfaces
+typealias A15<in K> = In<out K>
+              ^
+compiler/testData/cli/jvm/conflictingProjection.kt:19:23: error: projection is conflicting with variance of the corresponding type parameter of In<out K>. Remove the projection or replace it with '*'
+typealias A15<in K> = In<out K>
+                      ^
+COMPILATION_ERROR
diff --git a/compiler/testData/diagnostics/tests/declarationChecks/ConflictingAndRedundantProjections.fir.kt b/compiler/testData/diagnostics/tests/declarationChecks/ConflictingAndRedundantProjections.fir.kt
index c46a729de20..fe6c82df921 100644
--- a/compiler/testData/diagnostics/tests/declarationChecks/ConflictingAndRedundantProjections.fir.kt
+++ b/compiler/testData/diagnostics/tests/declarationChecks/ConflictingAndRedundantProjections.fir.kt
@@ -4,11 +4,11 @@ class Inv<T>
 class X
 
 fun f1(p: In<in X>) {}
-fun f2(p: In<out X>) {}
+fun f2(p: <!CONFLICTING_PROJECTION!>In<out X><!>) {}
 fun f3(p: In<X>) {}
 
 fun f4(p: Out<out X>) {}
-fun f5(p: Out<in X>) {}
+fun f5(p: <!CONFLICTING_PROJECTION!>Out<in X><!>) {}
 fun f6(p: Out<X>) {}
 
 fun f6(p: Inv<X>) {}
diff --git a/compiler/testData/diagnostics/tests/inference/kt39220.fir.kt b/compiler/testData/diagnostics/tests/inference/kt39220.fir.kt
index 30954aabfef..10dbcc218b1 100644
--- a/compiler/testData/diagnostics/tests/inference/kt39220.fir.kt
+++ b/compiler/testData/diagnostics/tests/inference/kt39220.fir.kt
@@ -51,7 +51,7 @@ val String.x1 get() = ""
 
 fun <K> bar1(f: KFunction2<K, String, String>) {}
 
-fun <K> bar2(f: KFunction2<out K, String, String>) {}
+fun <K> bar2(f: <!CONFLICTING_PROJECTION!>KFunction2<out K, String, String><!>) {}
 
 fun <K> bar3(f: Any?) {}
 
diff --git a/compiler/testData/diagnostics/tests/resolve/overloadConflicts/genericWithProjection.fir.kt b/compiler/testData/diagnostics/tests/resolve/overloadConflicts/genericWithProjection.fir.kt
index 0d0742be152..5b61a9298d8 100644
--- a/compiler/testData/diagnostics/tests/resolve/overloadConflicts/genericWithProjection.fir.kt
+++ b/compiler/testData/diagnostics/tests/resolve/overloadConflicts/genericWithProjection.fir.kt
@@ -7,5 +7,5 @@ class In<in T>() {
 
 fun test1(x: In<String>): Unit = x.f("1")
 fun test2(x: In<in String>): Unit = x.f("1")
-fun test3(x: In<out String>): Unit = x.f("1")
+fun test3(x: <!CONFLICTING_PROJECTION!>In<out String><!>): Unit = x.f("1")
 fun test4(x: In<*>): Unit = x.f("1")
\ No newline at end of file
diff --git a/compiler/testData/diagnostics/tests/typealias/conflictingProjections.fir.kt b/compiler/testData/diagnostics/tests/typealias/conflictingProjections.fir.kt
index eb078eb386a..03af30bf1f1 100644
--- a/compiler/testData/diagnostics/tests/typealias/conflictingProjections.fir.kt
+++ b/compiler/testData/diagnostics/tests/typealias/conflictingProjections.fir.kt
@@ -6,8 +6,8 @@ interface Out<out T>
 typealias InAlias<T> = In<T>
 typealias OutAlias<T> = Out<T>
 
-typealias TestOutForIn<T> = In<out T>
-typealias TestInForOut<T> = Out<in T>
+typealias TestOutForIn<T> = <!CONFLICTING_PROJECTION!>In<out T><!>
+typealias TestInForOut<T> = <!CONFLICTING_PROJECTION!>Out<in T><!>
 
 typealias TestOutForInWithinAlias<T> = InAlias<out T>
 typealias TestInForOutWithinAlias<T> = OutAlias<in T>
diff --git a/compiler/testData/diagnostics/tests/typealias/parameterRestrictions.fir.kt b/compiler/testData/diagnostics/tests/typealias/parameterRestrictions.fir.kt
index 8515a4b3cf4..d8e6cad4ce7 100644
--- a/compiler/testData/diagnostics/tests/typealias/parameterRestrictions.fir.kt
+++ b/compiler/testData/diagnostics/tests/typealias/parameterRestrictions.fir.kt
@@ -1,6 +1,6 @@
 // !DIAGNOSTICS: -UNUSED_TYPEALIAS_PARAMETER
 
-typealias WithVariance<in X, out Y> = Int
+typealias WithVariance<<!VARIANCE_ON_TYPE_PARAMETER_NOT_ALLOWED!>in X<!>, <!VARIANCE_ON_TYPE_PARAMETER_NOT_ALLOWED!>out Y<!>> = Int
 typealias WithBounds1<T : T> = Int
 typealias WithBounds2<X : Y, Y : X> = Int
 
diff --git a/compiler/testData/diagnostics/tests/typealias/substitutionVariance.fir.kt b/compiler/testData/diagnostics/tests/typealias/substitutionVariance.fir.kt
index bb31c55e0fc..351a2a1ab03 100644
--- a/compiler/testData/diagnostics/tests/typealias/substitutionVariance.fir.kt
+++ b/compiler/testData/diagnostics/tests/typealias/substitutionVariance.fir.kt
@@ -6,11 +6,11 @@ class Inv<T>
 
 typealias In1<T> = In<T>
 typealias In2<T> = In<in T>
-typealias In3<T> = In<out T>
+typealias In3<T> = <!CONFLICTING_PROJECTION!>In<out T><!>
 typealias In4<T> = In<*>
 
 typealias Out1<T> = Out<T>
-typealias Out2<T> = Out<in T>
+typealias Out2<T> = <!CONFLICTING_PROJECTION!>Out<in T><!>
 typealias Out3<T> = Out<out T>
 typealias Out4<T> = Out<*>
 
diff --git a/compiler/testData/diagnostics/tests/variance/InPosition.fir.kt b/compiler/testData/diagnostics/tests/variance/InPosition.fir.kt
index 9e3122e26e6..78d0051f8d3 100644
--- a/compiler/testData/diagnostics/tests/variance/InPosition.fir.kt
+++ b/compiler/testData/diagnostics/tests/variance/InPosition.fir.kt
@@ -35,7 +35,7 @@ interface Test<in I, out O, P> {
     fun neOk6(i: In<In<O>>)
     fun neOk7(i: Pair<In<I>, O>)
     fun neOk8(i: Inv<out O>)
-    fun neOk9(i: In<out P>)
+    fun neOk9(i: <!CONFLICTING_PROJECTION!>In<out P><!>)
     fun neOk10(i: Out<O>)
 
     fun neOk11(i: Inv<in I>)
diff --git a/compiler/testData/diagnostics/tests/variance/InvariantPosition.fir.kt b/compiler/testData/diagnostics/tests/variance/InvariantPosition.fir.kt
index 6d68d795ae3..31f2c5717d5 100644
--- a/compiler/testData/diagnostics/tests/variance/InvariantPosition.fir.kt
+++ b/compiler/testData/diagnostics/tests/variance/InvariantPosition.fir.kt
@@ -23,7 +23,7 @@ interface Test<in I, out O, P> {
     var neOk7: Pair<In<I>, O>
     var neOk8: Inv<in O>
     var neOk9: Inv<in I>
-    var neOk10: In<out I>
+    var neOk10: <!CONFLICTING_PROJECTION!>In<out I><!>
 
     var neOk11: I
     var neOk12: In<O>
diff --git a/compiler/testData/diagnostics/tests/variance/OutPosition.fir.kt b/compiler/testData/diagnostics/tests/variance/OutPosition.fir.kt
index f2cf351d677..3e048d33525 100644
--- a/compiler/testData/diagnostics/tests/variance/OutPosition.fir.kt
+++ b/compiler/testData/diagnostics/tests/variance/OutPosition.fir.kt
@@ -28,7 +28,7 @@ interface Test<in I, out O, P> {
     fun neOk5(): Inv<O>
     fun neOk6(): Pair<In<O>, I>
     fun neOk7(): Inv<in O>
-    fun neOk8(): Out<in I>
+    fun neOk8(): <!CONFLICTING_PROJECTION!>Out<in I><!>
     
     fun neOk10(): Inv<in O>
     fun neOk11(): Inv<out I>
diff --git a/compiler/tests/org/jetbrains/kotlin/cli/CliTestGenerated.java b/compiler/tests/org/jetbrains/kotlin/cli/CliTestGenerated.java
index be7b7c7e445..aea6cc1c486 100644
--- a/compiler/tests/org/jetbrains/kotlin/cli/CliTestGenerated.java
+++ b/compiler/tests/org/jetbrains/kotlin/cli/CliTestGenerated.java
@@ -140,6 +140,11 @@ public class CliTestGenerated extends AbstractCliTest {
             runTest("compiler/testData/cli/jvm/conflictingOverloads.args");
         }
 
+        @TestMetadata("conflictingProjection.args")
+        public void testConflictingProjection() throws Exception {
+            runTest("compiler/testData/cli/jvm/conflictingProjection.args");
+        }
+
         @TestMetadata("coroutinesEnable.args")
         public void testCoroutinesEnable() throws Exception {
             runTest("compiler/testData/cli/jvm/coroutinesEnable.args");