diff --git a/compiler/util/src/org/jetbrains/kotlin/config/LanguageVersionSettings.kt b/compiler/util/src/org/jetbrains/kotlin/config/LanguageVersionSettings.kt
index bf87811afb3..c69e51e1c0c 100644
--- a/compiler/util/src/org/jetbrains/kotlin/config/LanguageVersionSettings.kt
+++ b/compiler/util/src/org/jetbrains/kotlin/config/LanguageVersionSettings.kt
@@ -177,6 +177,8 @@ enum class LanguageFeature(
     SamWrapperClassesAreSynthetic(KOTLIN_1_5, defaultState = State.ENABLED, kind = BUG_FIX),
     StrictOnlyInputTypesChecks(KOTLIN_1_5),
 
+    JsEnableExtensionFunctionInExternals(KOTLIN_1_5, defaultState = State.DISABLED, kind = OTHER),
+
     // Disabled until the breaking change is approved by the committee, see KT-10884.
     PackagePrivateFileClassesWithAllPrivateMembers(KOTLIN_1_5, defaultState = State.DISABLED),
 
diff --git a/js/js.frontend/src/org/jetbrains/kotlin/js/resolve/diagnostics/JsExternalChecker.kt b/js/js.frontend/src/org/jetbrains/kotlin/js/resolve/diagnostics/JsExternalChecker.kt
index 837a7de21b6..8b0588f032c 100644
--- a/js/js.frontend/src/org/jetbrains/kotlin/js/resolve/diagnostics/JsExternalChecker.kt
+++ b/js/js.frontend/src/org/jetbrains/kotlin/js/resolve/diagnostics/JsExternalChecker.kt
@@ -7,6 +7,7 @@ package org.jetbrains.kotlin.js.resolve.diagnostics
 
 import org.jetbrains.kotlin.builtins.StandardNames
 import org.jetbrains.kotlin.builtins.isExtensionFunctionType
+import org.jetbrains.kotlin.config.LanguageFeature
 import org.jetbrains.kotlin.descriptors.*
 import org.jetbrains.kotlin.diagnostics.DiagnosticFactory0
 import org.jetbrains.kotlin.diagnostics.DiagnosticSink
@@ -119,7 +120,9 @@ object JsExternalChecker : DeclarationChecker {
         }
 
         reportOnParametersAndReturnTypesIf(ErrorsJs.INLINE_CLASS_IN_EXTERNAL_DECLARATION, KotlinType::isInlineClassType)
-        reportOnParametersAndReturnTypesIf(ErrorsJs.EXTENSION_FUNCTION_IN_EXTERNAL_DECLARATION, KotlinType::isExtensionFunctionType)
+        if (!context.languageVersionSettings.supportsFeature(LanguageFeature.JsEnableExtensionFunctionInExternals)) {
+            reportOnParametersAndReturnTypesIf(ErrorsJs.EXTENSION_FUNCTION_IN_EXTERNAL_DECLARATION, KotlinType::isExtensionFunctionType)
+        }
 
         if (descriptor is CallableMemberDescriptor && descriptor.isNonAbstractMemberOfInterface() &&
             !descriptor.isNullableProperty()