diff --git a/analysis/analysis-api-fir/src/org/jetbrains/kotlin/analysis/api/fir/diagnostics/KtFirDataClassConverters.kt b/analysis/analysis-api-fir/src/org/jetbrains/kotlin/analysis/api/fir/diagnostics/KtFirDataClassConverters.kt
index 6b2a81dbc18..7602dee9a47 100644
--- a/analysis/analysis-api-fir/src/org/jetbrains/kotlin/analysis/api/fir/diagnostics/KtFirDataClassConverters.kt
+++ b/analysis/analysis-api-fir/src/org/jetbrains/kotlin/analysis/api/fir/diagnostics/KtFirDataClassConverters.kt
@@ -2588,6 +2588,20 @@ internal val KT_DIAGNOSTIC_CONVERTER = KtDiagnosticConverterBuilder.buildConvert
             token,
         )
     }
+    add(FirErrors.MULTIPLE_DEFAULTS_INHERITED_FROM_SUPERTYPES) { firDiagnostic ->
+        MultipleDefaultsInheritedFromSupertypesImpl(
+            firSymbolBuilder.buildSymbol(firDiagnostic.a),
+            firDiagnostic as KtPsiDiagnostic,
+            token,
+        )
+    }
+    add(FirErrors.MULTIPLE_DEFAULTS_INHERITED_FROM_SUPERTYPES_WHEN_NO_EXPLICIT_OVERRIDE) { firDiagnostic ->
+        MultipleDefaultsInheritedFromSupertypesWhenNoExplicitOverrideImpl(
+            firSymbolBuilder.buildSymbol(firDiagnostic.a),
+            firDiagnostic as KtPsiDiagnostic,
+            token,
+        )
+    }
     add(FirErrors.TYPEALIAS_EXPANDS_TO_ARRAY_OF_NOTHINGS) { firDiagnostic ->
         TypealiasExpandsToArrayOfNothingsImpl(
             firSymbolBuilder.typeBuilder.buildKtType(firDiagnostic.a),
diff --git a/analysis/analysis-api-fir/src/org/jetbrains/kotlin/analysis/api/fir/diagnostics/KtFirDiagnostics.kt b/analysis/analysis-api-fir/src/org/jetbrains/kotlin/analysis/api/fir/diagnostics/KtFirDiagnostics.kt
index 150f4d42941..b79285406f7 100644
--- a/analysis/analysis-api-fir/src/org/jetbrains/kotlin/analysis/api/fir/diagnostics/KtFirDiagnostics.kt
+++ b/analysis/analysis-api-fir/src/org/jetbrains/kotlin/analysis/api/fir/diagnostics/KtFirDiagnostics.kt
@@ -1839,6 +1839,16 @@ sealed interface KtFirDiagnostic<PSI : PsiElement> : KtDiagnosticWithPsi<PSI> {
         val containingClassName: Name
     }
 
+    interface MultipleDefaultsInheritedFromSupertypes : KtFirDiagnostic<KtElement> {
+        override val diagnosticClass get() = MultipleDefaultsInheritedFromSupertypes::class
+        val valueParameter: KtSymbol
+    }
+
+    interface MultipleDefaultsInheritedFromSupertypesWhenNoExplicitOverride : KtFirDiagnostic<KtElement> {
+        override val diagnosticClass get() = MultipleDefaultsInheritedFromSupertypesWhenNoExplicitOverride::class
+        val valueParameter: KtSymbol
+    }
+
     interface TypealiasExpandsToArrayOfNothings : KtFirDiagnostic<KtElement> {
         override val diagnosticClass get() = TypealiasExpandsToArrayOfNothings::class
         val type: KtType
diff --git a/analysis/analysis-api-fir/src/org/jetbrains/kotlin/analysis/api/fir/diagnostics/KtFirDiagnosticsImpl.kt b/analysis/analysis-api-fir/src/org/jetbrains/kotlin/analysis/api/fir/diagnostics/KtFirDiagnosticsImpl.kt
index efe071dda04..8ccb1b960c1 100644
--- a/analysis/analysis-api-fir/src/org/jetbrains/kotlin/analysis/api/fir/diagnostics/KtFirDiagnosticsImpl.kt
+++ b/analysis/analysis-api-fir/src/org/jetbrains/kotlin/analysis/api/fir/diagnostics/KtFirDiagnosticsImpl.kt
@@ -2209,6 +2209,18 @@ internal class CannotChangeAccessPrivilegeImpl(
     token: KtLifetimeToken,
 ) : KtAbstractFirDiagnostic<KtModifierListOwner>(firDiagnostic, token), KtFirDiagnostic.CannotChangeAccessPrivilege
 
+internal class MultipleDefaultsInheritedFromSupertypesImpl(
+    override val valueParameter: KtSymbol,
+    firDiagnostic: KtPsiDiagnostic,
+    token: KtLifetimeToken,
+) : KtAbstractFirDiagnostic<KtElement>(firDiagnostic, token), KtFirDiagnostic.MultipleDefaultsInheritedFromSupertypes
+
+internal class MultipleDefaultsInheritedFromSupertypesWhenNoExplicitOverrideImpl(
+    override val valueParameter: KtSymbol,
+    firDiagnostic: KtPsiDiagnostic,
+    token: KtLifetimeToken,
+) : KtAbstractFirDiagnostic<KtElement>(firDiagnostic, token), KtFirDiagnostic.MultipleDefaultsInheritedFromSupertypesWhenNoExplicitOverride
+
 internal class TypealiasExpandsToArrayOfNothingsImpl(
     override val type: KtType,
     firDiagnostic: KtPsiDiagnostic,
diff --git a/compiler/fir/checkers/checkers-component-generator/src/org/jetbrains/kotlin/fir/checkers/generator/diagnostics/FirDiagnosticsList.kt b/compiler/fir/checkers/checkers-component-generator/src/org/jetbrains/kotlin/fir/checkers/generator/diagnostics/FirDiagnosticsList.kt
index 019ca2bb104..deb74b0bcb8 100644
--- a/compiler/fir/checkers/checkers-component-generator/src/org/jetbrains/kotlin/fir/checkers/generator/diagnostics/FirDiagnosticsList.kt
+++ b/compiler/fir/checkers/checkers-component-generator/src/org/jetbrains/kotlin/fir/checkers/generator/diagnostics/FirDiagnosticsList.kt
@@ -882,6 +882,13 @@ object DIAGNOSTICS_LIST : DiagnosticList("FirErrors") {
             parameter<Name>("containingClassName")
         }
 
+        val MULTIPLE_DEFAULTS_INHERITED_FROM_SUPERTYPES by error<KtElement>(PositioningStrategy.DECLARATION_SIGNATURE_OR_DEFAULT) {
+            parameter<FirValueParameterSymbol>("valueParameter")
+        }
+        val MULTIPLE_DEFAULTS_INHERITED_FROM_SUPERTYPES_WHEN_NO_EXPLICIT_OVERRIDE by error<KtElement>(PositioningStrategy.DECLARATION_NAME) {
+            parameter<FirValueParameterSymbol>("valueParameter")
+        }
+
         val TYPEALIAS_EXPANDS_TO_ARRAY_OF_NOTHINGS by error<KtElement> {
             parameter<ConeKotlinType>("type")
         }
diff --git a/compiler/fir/checkers/gen/org/jetbrains/kotlin/fir/analysis/diagnostics/FirErrors.kt b/compiler/fir/checkers/gen/org/jetbrains/kotlin/fir/analysis/diagnostics/FirErrors.kt
index 1d22faaad9c..2c7c391aa59 100644
--- a/compiler/fir/checkers/gen/org/jetbrains/kotlin/fir/analysis/diagnostics/FirErrors.kt
+++ b/compiler/fir/checkers/gen/org/jetbrains/kotlin/fir/analysis/diagnostics/FirErrors.kt
@@ -489,6 +489,8 @@ object FirErrors {
     val DATA_CLASS_OVERRIDE_DEFAULT_VALUES by error2<KtElement, FirCallableSymbol<*>, FirClassSymbol<*>>(SourceElementPositioningStrategies.DATA_MODIFIER)
     val CANNOT_WEAKEN_ACCESS_PRIVILEGE by error3<KtModifierListOwner, Visibility, FirCallableSymbol<*>, Name>(SourceElementPositioningStrategies.VISIBILITY_MODIFIER)
     val CANNOT_CHANGE_ACCESS_PRIVILEGE by error3<KtModifierListOwner, Visibility, FirCallableSymbol<*>, Name>(SourceElementPositioningStrategies.VISIBILITY_MODIFIER)
+    val MULTIPLE_DEFAULTS_INHERITED_FROM_SUPERTYPES by error1<KtElement, FirValueParameterSymbol>(SourceElementPositioningStrategies.DECLARATION_SIGNATURE_OR_DEFAULT)
+    val MULTIPLE_DEFAULTS_INHERITED_FROM_SUPERTYPES_WHEN_NO_EXPLICIT_OVERRIDE by error1<KtElement, FirValueParameterSymbol>(SourceElementPositioningStrategies.DECLARATION_NAME)
     val TYPEALIAS_EXPANDS_TO_ARRAY_OF_NOTHINGS by error1<KtElement, ConeKotlinType>()
     val OVERRIDING_FINAL_MEMBER by error2<KtNamedDeclaration, FirCallableSymbol<*>, Name>(SourceElementPositioningStrategies.OVERRIDE_MODIFIER)
     val RETURN_TYPE_MISMATCH_ON_INHERITANCE by error2<KtClassOrObject, FirCallableSymbol<*>, FirCallableSymbol<*>>(SourceElementPositioningStrategies.DECLARATION_NAME)
diff --git a/compiler/fir/checkers/gen/org/jetbrains/kotlin/fir/analysis/diagnostics/FirNonSuppressibleErrorNames.kt b/compiler/fir/checkers/gen/org/jetbrains/kotlin/fir/analysis/diagnostics/FirNonSuppressibleErrorNames.kt
index 3206b9c945e..70b0d040a79 100644
--- a/compiler/fir/checkers/gen/org/jetbrains/kotlin/fir/analysis/diagnostics/FirNonSuppressibleErrorNames.kt
+++ b/compiler/fir/checkers/gen/org/jetbrains/kotlin/fir/analysis/diagnostics/FirNonSuppressibleErrorNames.kt
@@ -323,6 +323,8 @@ val FIR_NON_SUPPRESSIBLE_ERROR_NAMES: Set<String> = setOf(
     "DATA_CLASS_OVERRIDE_DEFAULT_VALUES",
     "CANNOT_WEAKEN_ACCESS_PRIVILEGE",
     "CANNOT_CHANGE_ACCESS_PRIVILEGE",
+    "MULTIPLE_DEFAULTS_INHERITED_FROM_SUPERTYPES",
+    "MULTIPLE_DEFAULTS_INHERITED_FROM_SUPERTYPES_WHEN_NO_EXPLICIT_OVERRIDE",
     "TYPEALIAS_EXPANDS_TO_ARRAY_OF_NOTHINGS",
     "OVERRIDING_FINAL_MEMBER",
     "RETURN_TYPE_MISMATCH_ON_INHERITANCE",
diff --git a/compiler/fir/checkers/src/org/jetbrains/kotlin/fir/analysis/checkers/CommonDeclarationCheckers.kt b/compiler/fir/checkers/src/org/jetbrains/kotlin/fir/analysis/checkers/CommonDeclarationCheckers.kt
index 9c8a54a99bb..0e70ce53b2b 100644
--- a/compiler/fir/checkers/src/org/jetbrains/kotlin/fir/analysis/checkers/CommonDeclarationCheckers.kt
+++ b/compiler/fir/checkers/src/org/jetbrains/kotlin/fir/analysis/checkers/CommonDeclarationCheckers.kt
@@ -131,6 +131,7 @@ object CommonDeclarationCheckers : DeclarationCheckers() {
             FirOuterClassArgumentsRequiredChecker,
             FirPropertyInitializationChecker,
             FirDelegateFieldTypeMismatchChecker,
+            FirMultipleDefaultsInheritedFromSupertypesChecker,
             FirFiniteBoundRestrictionChecker,
         )
 
diff --git a/compiler/fir/checkers/src/org/jetbrains/kotlin/fir/analysis/checkers/FirHelpers.kt b/compiler/fir/checkers/src/org/jetbrains/kotlin/fir/analysis/checkers/FirHelpers.kt
index 9af4e3b828d..5a829ed82bf 100644
--- a/compiler/fir/checkers/src/org/jetbrains/kotlin/fir/analysis/checkers/FirHelpers.kt
+++ b/compiler/fir/checkers/src/org/jetbrains/kotlin/fir/analysis/checkers/FirHelpers.kt
@@ -28,11 +28,9 @@ import org.jetbrains.kotlin.fir.references.FirSuperReference
 import org.jetbrains.kotlin.fir.references.toResolvedCallableSymbol
 import org.jetbrains.kotlin.fir.resolve.*
 import org.jetbrains.kotlin.fir.resolve.providers.symbolProvider
-import org.jetbrains.kotlin.fir.scopes.FirTypeScope
-import org.jetbrains.kotlin.fir.scopes.getDirectOverriddenFunctions
+import org.jetbrains.kotlin.fir.scopes.*
+import org.jetbrains.kotlin.fir.scopes.impl.declaredMemberScope
 import org.jetbrains.kotlin.fir.scopes.impl.multipleDelegatesWithTheSameSignature
-import org.jetbrains.kotlin.fir.scopes.overriddenFunctions
-import org.jetbrains.kotlin.fir.scopes.unsubstitutedScope
 import org.jetbrains.kotlin.fir.symbols.ConeTypeParameterLookupTag
 import org.jetbrains.kotlin.fir.symbols.FirBasedSymbol
 import org.jetbrains.kotlin.fir.symbols.SymbolInternals
@@ -726,6 +724,33 @@ fun FirNamedFunctionSymbol.directOverriddenFunctions(session: FirSession, scopeS
 fun FirNamedFunctionSymbol.directOverriddenFunctions(context: CheckerContext) =
     directOverriddenFunctions(context.session, context.sessionHolder.scopeSession)
 
+inline fun <C : MutableCollection<FirNamedFunctionSymbol>> FirNamedFunctionSymbol.collectOverriddenFunctionsWhere(
+    collection: C,
+    context: CheckerContext,
+    crossinline condition: (FirNamedFunctionSymbol) -> Boolean,
+) = collection.apply {
+    processOverriddenFunctions(context) {
+        if (condition(it)) {
+            add(it)
+        }
+    }
+}
+
+inline fun FirNamedFunctionSymbol.processOverriddenFunctions(
+    context: CheckerContext,
+    crossinline action: (FirNamedFunctionSymbol) -> Unit,
+) {
+    val containingClass = getContainingClassSymbol(context.session) as? FirClassSymbol ?: return
+    val firTypeScope = containingClass.unsubstitutedScope(context)
+
+    firTypeScope.processFunctionsByName(callableId.callableName) { }
+
+    firTypeScope.processOverriddenFunctions(this) {
+        action(it)
+        ProcessorAction.NEXT
+    }
+}
+
 val CheckerContext.closestNonLocal get() = containingDeclarations.takeWhile { it.isNonLocal }.lastOrNull()
 
 fun CheckerContext.closestNonLocalWith(declaration: FirDeclaration) =
diff --git a/compiler/fir/checkers/src/org/jetbrains/kotlin/fir/analysis/checkers/declaration/FirMultipleDefaultsInheritedFromSupertypesChecker.kt b/compiler/fir/checkers/src/org/jetbrains/kotlin/fir/analysis/checkers/declaration/FirMultipleDefaultsInheritedFromSupertypesChecker.kt
new file mode 100644
index 00000000000..d4f9489acd1
--- /dev/null
+++ b/compiler/fir/checkers/src/org/jetbrains/kotlin/fir/analysis/checkers/declaration/FirMultipleDefaultsInheritedFromSupertypesChecker.kt
@@ -0,0 +1,67 @@
+/*
+ * Copyright 2010-2023 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.diagnostics.DiagnosticReporter
+import org.jetbrains.kotlin.diagnostics.reportOn
+import org.jetbrains.kotlin.fir.analysis.checkers.collectOverriddenFunctionsWhere
+import org.jetbrains.kotlin.fir.analysis.checkers.context.CheckerContext
+import org.jetbrains.kotlin.fir.analysis.checkers.unsubstitutedScope
+import org.jetbrains.kotlin.fir.analysis.diagnostics.FirErrors
+import org.jetbrains.kotlin.fir.containingClassLookupTag
+import org.jetbrains.kotlin.fir.declarations.FirDeclarationOrigin
+import org.jetbrains.kotlin.fir.declarations.FirRegularClass
+import org.jetbrains.kotlin.fir.declarations.utils.superConeTypes
+import org.jetbrains.kotlin.fir.isSubstitutionOverride
+import org.jetbrains.kotlin.fir.scopes.processAllFunctions
+import org.jetbrains.kotlin.fir.symbols.impl.FirNamedFunctionSymbol
+
+object FirMultipleDefaultsInheritedFromSupertypesChecker : FirRegularClassChecker() {
+    override fun check(declaration: FirRegularClass, context: CheckerContext, reporter: DiagnosticReporter) {
+        declaration.unsubstitutedScope(context).processAllFunctions {
+            if (it.containingClassLookupTag() != declaration.symbol.toLookupTag()) {
+                return@processAllFunctions
+            }
+
+            checkFunction(declaration, it, context, reporter)
+        }
+    }
+
+    private fun checkFunction(
+        declaration: FirRegularClass,
+        function: FirNamedFunctionSymbol,
+        context: CheckerContext,
+        reporter: DiagnosticReporter,
+    ) {
+        val overriddenFunctions = function.collectOverriddenFunctionsWhere(mutableSetOf(), context) { overridden ->
+            // Substitution overrides copy default values from originals
+            !overridden.isSubstitutionOverride && overridden.valueParameterSymbols.any { it.hasDefaultValue }
+        }
+        val isExplicitOverride = function.origin == FirDeclarationOrigin.Source
+
+        for ((index, parameter) in function.valueParameterSymbols.withIndex()) {
+            val basesWithDefaultValues = overriddenFunctions.count { it.valueParameterSymbols[index].hasDefaultValue }
+
+            when {
+                basesWithDefaultValues <= 1 -> {
+                    continue
+                }
+                !isExplicitOverride -> {
+                    reporter.reportOn(
+                        declaration.source, FirErrors.MULTIPLE_DEFAULTS_INHERITED_FROM_SUPERTYPES_WHEN_NO_EXPLICIT_OVERRIDE,
+                        parameter, context,
+                    )
+                    // Avoid duplicates
+                    break
+                }
+                else -> reporter.reportOn(
+                    parameter.source, FirErrors.MULTIPLE_DEFAULTS_INHERITED_FROM_SUPERTYPES,
+                    parameter, context,
+                )
+            }
+        }
+    }
+}
diff --git a/compiler/fir/checkers/src/org/jetbrains/kotlin/fir/analysis/diagnostics/FirErrorsDefaultMessages.kt b/compiler/fir/checkers/src/org/jetbrains/kotlin/fir/analysis/diagnostics/FirErrorsDefaultMessages.kt
index 2a505999b51..3cf57033c6d 100644
--- a/compiler/fir/checkers/src/org/jetbrains/kotlin/fir/analysis/diagnostics/FirErrorsDefaultMessages.kt
+++ b/compiler/fir/checkers/src/org/jetbrains/kotlin/fir/analysis/diagnostics/FirErrorsDefaultMessages.kt
@@ -367,6 +367,8 @@ import org.jetbrains.kotlin.fir.analysis.diagnostics.FirErrors.MIXING_SUSPEND_AN
 import org.jetbrains.kotlin.fir.analysis.diagnostics.FirErrors.MODIFIER_FORM_FOR_NON_BUILT_IN_SUSPEND
 import org.jetbrains.kotlin.fir.analysis.diagnostics.FirErrors.MODIFIER_FORM_FOR_NON_BUILT_IN_SUSPEND_FUN
 import org.jetbrains.kotlin.fir.analysis.diagnostics.FirErrors.MULTIPLE_ARGUMENTS_APPLICABLE_FOR_CONTEXT_RECEIVER
+import org.jetbrains.kotlin.fir.analysis.diagnostics.FirErrors.MULTIPLE_DEFAULTS_INHERITED_FROM_SUPERTYPES
+import org.jetbrains.kotlin.fir.analysis.diagnostics.FirErrors.MULTIPLE_DEFAULTS_INHERITED_FROM_SUPERTYPES_WHEN_NO_EXPLICIT_OVERRIDE
 import org.jetbrains.kotlin.fir.analysis.diagnostics.FirErrors.MULTIPLE_VARARG_PARAMETERS
 import org.jetbrains.kotlin.fir.analysis.diagnostics.FirErrors.MULTI_FIELD_VALUE_CLASS_PRIMARY_CONSTRUCTOR_DEFAULT_PARAMETER
 import org.jetbrains.kotlin.fir.analysis.diagnostics.FirErrors.MUST_BE_INITIALIZED
@@ -1492,6 +1494,10 @@ object FirErrorsDefaultMessages : BaseDiagnosticRendererFactory() {
             FQ_NAMES_IN_TYPES
         )
 
+        val multipleDefaultsMessage = "More than one overridden descriptor declares a default value for ''{0}''. As the compiler can not make sure these values agree, this is not allowed."
+        map.put(MULTIPLE_DEFAULTS_INHERITED_FROM_SUPERTYPES, multipleDefaultsMessage, SYMBOL)
+        map.put(MULTIPLE_DEFAULTS_INHERITED_FROM_SUPERTYPES_WHEN_NO_EXPLICIT_OVERRIDE, multipleDefaultsMessage, SYMBOL)
+
         map.put(TYPEALIAS_EXPANDS_TO_ARRAY_OF_NOTHINGS, "Type alias expanded to malformed type ''{0}''", RENDER_TYPE)
 
         map.put(OVERRIDING_FINAL_MEMBER, "''{0}'' in ''{1}'' is final and cannot be overridden.", DECLARATION_NAME, TO_STRING)
diff --git a/compiler/testData/codegen/box/bridges/kt46389.kt b/compiler/testData/codegen/box/bridges/kt46389.kt
index c93a0bf7c85..5befdb2679b 100644
--- a/compiler/testData/codegen/box/bridges/kt46389.kt
+++ b/compiler/testData/codegen/box/bridges/kt46389.kt
@@ -1,4 +1,6 @@
-// IGNORE_BACKEND: JS, JS_IR, JS_IR_ES6
+// IGNORE_BACKEND_K1: JS, JS_IR, JS_IR_ES6
+// IGNORE_BACKEND_K2: ANY
+// STATUS: This must be red code anyway, KT-36188
 
 // The code in this test should be prohibited in the frontend, see KT-36188.
 
diff --git a/compiler/testData/codegen/box/bridges/kt46389_jvmDefault.kt b/compiler/testData/codegen/box/bridges/kt46389_jvmDefault.kt
index 6cfebf67867..b0ff276453f 100644
--- a/compiler/testData/codegen/box/bridges/kt46389_jvmDefault.kt
+++ b/compiler/testData/codegen/box/bridges/kt46389_jvmDefault.kt
@@ -1,4 +1,6 @@
-// IGNORE_BACKEND: JS, JS_IR, JS_IR_ES6
+// IGNORE_BACKEND_K1: JS, JS_IR, JS_IR_ES6
+// IGNORE_BACKEND_K2: ANY
+// STATUS: This must be red code anyway, KT-36188
 // !JVM_DEFAULT_MODE: all
 // JVM_TARGET: 1.8
 
diff --git a/compiler/testData/codegen/box/defaultArguments/function/kt36188.kt b/compiler/testData/codegen/box/defaultArguments/function/kt36188.kt
index 5ed4b2a43cf..a343c768284 100644
--- a/compiler/testData/codegen/box/defaultArguments/function/kt36188.kt
+++ b/compiler/testData/codegen/box/defaultArguments/function/kt36188.kt
@@ -1,4 +1,6 @@
 // IGNORE_BACKEND: JS
+// IGNORE_BACKEND_K2: ANY
+// STATUS: This must be red code anyway, KT-36188
 
 // Test for KT-36188 bug compatibility between non-IR and IR backends
 
diff --git a/compiler/testData/codegen/box/defaultArguments/function/kt36188_2.kt b/compiler/testData/codegen/box/defaultArguments/function/kt36188_2.kt
index e0bb2edad07..20f91488640 100644
--- a/compiler/testData/codegen/box/defaultArguments/function/kt36188_2.kt
+++ b/compiler/testData/codegen/box/defaultArguments/function/kt36188_2.kt
@@ -1,4 +1,6 @@
 // IGNORE_BACKEND: JS
+// IGNORE_BACKEND_K2: ANY
+// STATUS: This must be red code anyway, KT-36188
 
 // Test for KT-36188 bug compatibility between non-IR and IR backends
 
diff --git a/compiler/testData/diagnostics/tests/annotations/rendering/multipleInheritedDefaults.fir.kt b/compiler/testData/diagnostics/tests/annotations/rendering/multipleInheritedDefaults.fir.kt
index 646f648ff0b..3d32fe44823 100644
--- a/compiler/testData/diagnostics/tests/annotations/rendering/multipleInheritedDefaults.fir.kt
+++ b/compiler/testData/diagnostics/tests/annotations/rendering/multipleInheritedDefaults.fir.kt
@@ -17,10 +17,10 @@ interface B {
     fun foo(@An a: @An Int = @An 2)
 }
 
-class AB1 : A, B
+<!MULTIPLE_DEFAULTS_INHERITED_FROM_SUPERTYPES_WHEN_NO_EXPLICIT_OVERRIDE("@An() a: @R|An|()  Int = ...")!>class AB1<!> : A, B
 
 @An
 class AB2 : A, B {
     @An
-    override fun foo(@An a: @An Int) {}
+    override fun foo(<!MULTIPLE_DEFAULTS_INHERITED_FROM_SUPERTYPES("@An() a: @R|An|()  Int")!>@An a: @An Int<!>) {}
 }
\ No newline at end of file
diff --git a/compiler/testData/diagnostics/tests/falseNegativeDuplicateDefaultValues1.fir.kt b/compiler/testData/diagnostics/tests/falseNegativeDuplicateDefaultValues1.fir.kt
new file mode 100644
index 00000000000..53f7e504e7b
--- /dev/null
+++ b/compiler/testData/diagnostics/tests/falseNegativeDuplicateDefaultValues1.fir.kt
@@ -0,0 +1,15 @@
+// ISSUE: KT-36188
+
+interface SomeRandomBase<K> {
+    fun child(props: Int = 20)
+}
+
+interface SomeRandomOverride<J> : SomeRandomBase<J>
+
+open class Keker<P> {
+    open fun child(props: Int = 10) {}
+}
+
+class Implementation<P>() : Keker<P>(), SomeRandomOverride<P> {
+    override fun child(<!MULTIPLE_DEFAULTS_INHERITED_FROM_SUPERTYPES!>props: Int<!>) {}
+}
diff --git a/compiler/testData/diagnostics/tests/falseNegativeDuplicateDefaultValues1.kt b/compiler/testData/diagnostics/tests/falseNegativeDuplicateDefaultValues1.kt
index fe48226f0c2..88d2d6073a0 100644
--- a/compiler/testData/diagnostics/tests/falseNegativeDuplicateDefaultValues1.kt
+++ b/compiler/testData/diagnostics/tests/falseNegativeDuplicateDefaultValues1.kt
@@ -1,4 +1,3 @@
-// FIR_IDENTICAL
 // ISSUE: KT-36188
 
 interface SomeRandomBase<K> {
diff --git a/compiler/testData/diagnostics/tests/falseNegativeDuplicateDefaultValues2.fir.kt b/compiler/testData/diagnostics/tests/falseNegativeDuplicateDefaultValues2.fir.kt
new file mode 100644
index 00000000000..bcbc3eb98fc
--- /dev/null
+++ b/compiler/testData/diagnostics/tests/falseNegativeDuplicateDefaultValues2.fir.kt
@@ -0,0 +1,17 @@
+// ISSUE: KT-36188
+
+interface SomeRandomBase<K> {
+    fun child(props: Int = 20)
+}
+
+interface SomeRandomOverride<J> : SomeRandomBase<J> {
+    override fun child(props: Int) {}
+}
+
+open class Keker<P> {
+    open fun child(props: Int = 10) {}
+}
+
+class Implementation<P>() : Keker<P>(), SomeRandomOverride<P> {
+    override fun child(<!MULTIPLE_DEFAULTS_INHERITED_FROM_SUPERTYPES!>props: Int<!>) {}
+}
diff --git a/compiler/testData/diagnostics/tests/falseNegativeDuplicateDefaultValues2.kt b/compiler/testData/diagnostics/tests/falseNegativeDuplicateDefaultValues2.kt
index a3df2c872b2..cb422eef183 100644
--- a/compiler/testData/diagnostics/tests/falseNegativeDuplicateDefaultValues2.kt
+++ b/compiler/testData/diagnostics/tests/falseNegativeDuplicateDefaultValues2.kt
@@ -1,4 +1,3 @@
-// FIR_IDENTICAL
 // ISSUE: KT-36188
 
 interface SomeRandomBase<K> {
diff --git a/compiler/testData/diagnostics/tests/falseNegativeDuplicateDefaultValues3.fir.kt b/compiler/testData/diagnostics/tests/falseNegativeDuplicateDefaultValues3.fir.kt
new file mode 100644
index 00000000000..4a89bb8f708
--- /dev/null
+++ b/compiler/testData/diagnostics/tests/falseNegativeDuplicateDefaultValues3.fir.kt
@@ -0,0 +1,17 @@
+// ISSUE: KT-36188
+
+interface SomeRandomBase<K> {
+    fun child(props: Int = 20)
+}
+
+interface SomeRandomOverride<J> : SomeRandomBase<J> {
+    override abstract fun child(props: Int)
+}
+
+open class Keker<P> {
+    open fun child(props: Int = 10) {}
+}
+
+class Implementation<P>() : Keker<P>(), SomeRandomOverride<P> {
+    override fun child(<!MULTIPLE_DEFAULTS_INHERITED_FROM_SUPERTYPES!>props: Int<!>) {}
+}
diff --git a/compiler/testData/diagnostics/tests/falseNegativeDuplicateDefaultValues3.kt b/compiler/testData/diagnostics/tests/falseNegativeDuplicateDefaultValues3.kt
index e7b003474d2..1a2373dced6 100644
--- a/compiler/testData/diagnostics/tests/falseNegativeDuplicateDefaultValues3.kt
+++ b/compiler/testData/diagnostics/tests/falseNegativeDuplicateDefaultValues3.kt
@@ -1,4 +1,3 @@
-// FIR_IDENTICAL
 // ISSUE: KT-36188
 
 interface SomeRandomBase<K> {
diff --git a/compiler/testData/diagnostics/tests/multipleDefaultsNoSource.fir.kt b/compiler/testData/diagnostics/tests/multipleDefaultsNoSource.fir.kt
index 20e29e31c34..8d98d8209a0 100644
--- a/compiler/testData/diagnostics/tests/multipleDefaultsNoSource.fir.kt
+++ b/compiler/testData/diagnostics/tests/multipleDefaultsNoSource.fir.kt
@@ -10,5 +10,5 @@ interface Y {
 
 object YImpl : Y
 
-<!DELEGATED_MEMBER_HIDES_SUPERTYPE_OVERRIDE!>class Z1<!> : X, Y by YImpl {}
-<!DELEGATED_MEMBER_HIDES_SUPERTYPE_OVERRIDE!>object Z1O<!> : X, Y by YImpl {}
+<!DELEGATED_MEMBER_HIDES_SUPERTYPE_OVERRIDE, MULTIPLE_DEFAULTS_INHERITED_FROM_SUPERTYPES_WHEN_NO_EXPLICIT_OVERRIDE!>class Z1<!> : X, Y by YImpl {}
+<!DELEGATED_MEMBER_HIDES_SUPERTYPE_OVERRIDE, MULTIPLE_DEFAULTS_INHERITED_FROM_SUPERTYPES_WHEN_NO_EXPLICIT_OVERRIDE!>object Z1O<!> : X, Y by YImpl {}
diff --git a/compiler/testData/diagnostics/tests/override/MultipleDefaultParametersInSupertypes.fir.kt b/compiler/testData/diagnostics/tests/override/MultipleDefaultParametersInSupertypes.fir.kt
deleted file mode 100644
index 4de8d35e241..00000000000
--- a/compiler/testData/diagnostics/tests/override/MultipleDefaultParametersInSupertypes.fir.kt
+++ /dev/null
@@ -1,15 +0,0 @@
-interface X {
-    fun foo(a : Int = 1)
-}
-
-interface Y {
-    fun foo(a : Int = 1)
-}
-
-class Z : X, Y {
-    override fun foo(a : Int) {}
-}
-
-object ZO : X, Y {
-    override fun foo(a : Int) {}
-}
\ No newline at end of file
diff --git a/compiler/testData/diagnostics/tests/override/MultipleDefaultParametersInSupertypes.kt b/compiler/testData/diagnostics/tests/override/MultipleDefaultParametersInSupertypes.kt
index f6aa6986f7c..aabe3c64642 100644
--- a/compiler/testData/diagnostics/tests/override/MultipleDefaultParametersInSupertypes.kt
+++ b/compiler/testData/diagnostics/tests/override/MultipleDefaultParametersInSupertypes.kt
@@ -1,3 +1,4 @@
+// FIR_IDENTICAL
 interface X {
     fun foo(a : Int = 1)
 }
diff --git a/compiler/testData/diagnostics/tests/override/MultipleDefaultParametersInSupertypesNoOverride.fir.kt b/compiler/testData/diagnostics/tests/override/MultipleDefaultParametersInSupertypesNoOverride.fir.kt
new file mode 100644
index 00000000000..f1de2a8d1aa
--- /dev/null
+++ b/compiler/testData/diagnostics/tests/override/MultipleDefaultParametersInSupertypesNoOverride.fir.kt
@@ -0,0 +1,15 @@
+interface X {
+    fun foo(a : Int = 1)
+}
+
+interface Y {
+    fun foo(a : Int = 1)
+}
+
+class Z : X, Y {
+    fun <!VIRTUAL_MEMBER_HIDDEN!>foo<!>(<!MULTIPLE_DEFAULTS_INHERITED_FROM_SUPERTYPES!>a : Int<!>) {}
+}
+
+object ZO : X, Y {
+    fun <!VIRTUAL_MEMBER_HIDDEN!>foo<!>(<!MULTIPLE_DEFAULTS_INHERITED_FROM_SUPERTYPES!>a : Int<!>) {}
+}
\ No newline at end of file
diff --git a/compiler/testData/diagnostics/tests/override/MultipleDefaultParametersInSupertypesNoOverride.kt b/compiler/testData/diagnostics/tests/override/MultipleDefaultParametersInSupertypesNoOverride.kt
index fd03fbcc64d..f7160d06304 100644
--- a/compiler/testData/diagnostics/tests/override/MultipleDefaultParametersInSupertypesNoOverride.kt
+++ b/compiler/testData/diagnostics/tests/override/MultipleDefaultParametersInSupertypesNoOverride.kt
@@ -1,4 +1,3 @@
-// FIR_IDENTICAL
 interface X {
     fun foo(a : Int = 1)
 }
diff --git a/compiler/testData/diagnostics/tests/override/MultipleDefaultsAndNamesInSupertypes.fir.kt b/compiler/testData/diagnostics/tests/override/MultipleDefaultsAndNamesInSupertypes.fir.kt
index 5a99fa791e6..775e199e75b 100644
--- a/compiler/testData/diagnostics/tests/override/MultipleDefaultsAndNamesInSupertypes.fir.kt
+++ b/compiler/testData/diagnostics/tests/override/MultipleDefaultsAndNamesInSupertypes.fir.kt
@@ -11,4 +11,4 @@ interface C {
 }
 
 // TODO DIFFERENT_NAMES_FOR_THE_SAME_PARAMETER_IN_SUPERTYPES reported twice
-class Z : A, B(), C
\ No newline at end of file
+<!MULTIPLE_DEFAULTS_INHERITED_FROM_SUPERTYPES_WHEN_NO_EXPLICIT_OVERRIDE!>class Z<!> : A, B(), C
diff --git a/compiler/testData/diagnostics/tests/override/MultipleDefaultsInSupertypesNoExplicitOverride.fir.kt b/compiler/testData/diagnostics/tests/override/MultipleDefaultsInSupertypesNoExplicitOverride.fir.kt
deleted file mode 100644
index fb7b2d1e764..00000000000
--- a/compiler/testData/diagnostics/tests/override/MultipleDefaultsInSupertypesNoExplicitOverride.fir.kt
+++ /dev/null
@@ -1,10 +0,0 @@
-interface X {
-    fun foo(a : Int = 1)
-}
-
-interface Y {
-    fun foo(a : Int = 1)
-}
-
-<!ABSTRACT_MEMBER_NOT_IMPLEMENTED!>class Z1<!> : X, Y {} // BUG
-<!ABSTRACT_MEMBER_NOT_IMPLEMENTED!>object Z1O<!> : X, Y {} // BUG
diff --git a/compiler/testData/diagnostics/tests/override/MultipleDefaultsInSupertypesNoExplicitOverride.kt b/compiler/testData/diagnostics/tests/override/MultipleDefaultsInSupertypesNoExplicitOverride.kt
index cf5ffb10eeb..29379af071f 100644
--- a/compiler/testData/diagnostics/tests/override/MultipleDefaultsInSupertypesNoExplicitOverride.kt
+++ b/compiler/testData/diagnostics/tests/override/MultipleDefaultsInSupertypesNoExplicitOverride.kt
@@ -1,3 +1,4 @@
+// FIR_IDENTICAL
 interface X {
     fun foo(a : Int = 1)
 }