diff --git a/analysis/low-level-api-fir/src/org/jetbrains/kotlin/analysis/low/level/api/fir/project/structure/sessionFactoryHelpers.kt b/analysis/low-level-api-fir/src/org/jetbrains/kotlin/analysis/low/level/api/fir/project/structure/sessionFactoryHelpers.kt
index a8b1e573473..fab1ceb8524 100644
--- a/analysis/low-level-api-fir/src/org/jetbrains/kotlin/analysis/low/level/api/fir/project/structure/sessionFactoryHelpers.kt
+++ b/analysis/low-level-api-fir/src/org/jetbrains/kotlin/analysis/low/level/api/fir/project/structure/sessionFactoryHelpers.kt
@@ -54,13 +54,10 @@ internal inline fun createCompositeSymbolProvider(
 internal fun FirSession.registerCompilerPluginExtensions(project: Project, module: KtSourceModule) {
     val extensionProvider = project.getService(KtCompilerPluginsProvider::class.java) ?: return
     FirSessionConfigurator(this).apply {
-        @Suppress("UNCHECKED_CAST")
-        val registrars = extensionProvider.getRegisteredExtensions(
-            module,
-            FirExtensionRegistrarAdapter,
-        ) as List<FirExtensionRegistrar>
+        val registrars = FirExtensionRegistrarAdapter.getInstances(project) +
+                extensionProvider.getRegisteredExtensions(module, FirExtensionRegistrarAdapter)
         for (extensionRegistrar in registrars) {
-            registerExtensions(extensionRegistrar.configure())
+            registerExtensions((extensionRegistrar as FirExtensionRegistrar).configure())
         }
     }.configure()
 }
diff --git a/analysis/low-level-api-fir/tests/org/jetbrains/kotlin/analysis/low/level/api/fir/services/KtCompilerPluginsProviderForTests.kt b/analysis/low-level-api-fir/tests/org/jetbrains/kotlin/analysis/low/level/api/fir/services/NoOpKtCompilerPluginsProvider.kt
similarity index 75%
rename from analysis/low-level-api-fir/tests/org/jetbrains/kotlin/analysis/low/level/api/fir/services/KtCompilerPluginsProviderForTests.kt
rename to analysis/low-level-api-fir/tests/org/jetbrains/kotlin/analysis/low/level/api/fir/services/NoOpKtCompilerPluginsProvider.kt
index 6f7de0d363c..802cc4934cf 100644
--- a/analysis/low-level-api-fir/tests/org/jetbrains/kotlin/analysis/low/level/api/fir/services/KtCompilerPluginsProviderForTests.kt
+++ b/analysis/low-level-api-fir/tests/org/jetbrains/kotlin/analysis/low/level/api/fir/services/NoOpKtCompilerPluginsProvider.kt
@@ -5,13 +5,11 @@
 
 package org.jetbrains.kotlin.analysis.low.level.api.fir.services
 
-import com.intellij.openapi.project.Project
 import org.jetbrains.kotlin.analysis.project.structure.KtCompilerPluginsProvider
 import org.jetbrains.kotlin.analysis.project.structure.KtSourceModule
 import org.jetbrains.kotlin.extensions.ProjectExtensionDescriptor
 
-internal class KtCompilerPluginsProviderForTests(val project: Project) : KtCompilerPluginsProvider() {
-    override fun <T : Any> getRegisteredExtensions(module: KtSourceModule, extensionType: ProjectExtensionDescriptor<T>): List<T> {
-        return extensionType.getInstances(project)
-    }
+internal object NoOpKtCompilerPluginsProvider : KtCompilerPluginsProvider() {
+    override fun <T : Any> getRegisteredExtensions(module: KtSourceModule, extensionType: ProjectExtensionDescriptor<T>): List<T> =
+        emptyList()
 }
diff --git a/analysis/low-level-api-fir/tests/org/jetbrains/kotlin/analysis/low/level/api/fir/test/base/AnalysisApiFirTestServiceRegistrar.kt b/analysis/low-level-api-fir/tests/org/jetbrains/kotlin/analysis/low/level/api/fir/test/base/AnalysisApiFirTestServiceRegistrar.kt
index 9cb13988726..e3199f9b6e6 100644
--- a/analysis/low-level-api-fir/tests/org/jetbrains/kotlin/analysis/low/level/api/fir/test/base/AnalysisApiFirTestServiceRegistrar.kt
+++ b/analysis/low-level-api-fir/tests/org/jetbrains/kotlin/analysis/low/level/api/fir/test/base/AnalysisApiFirTestServiceRegistrar.kt
@@ -17,7 +17,7 @@ import org.jetbrains.kotlin.analysis.low.level.api.fir.LLFirGlobalResolveCompone
 import org.jetbrains.kotlin.analysis.low.level.api.fir.LLFirResolveSessionService
 import org.jetbrains.kotlin.analysis.low.level.api.fir.api.services.FirSealedClassInheritorsProcessorFactory
 import org.jetbrains.kotlin.analysis.low.level.api.fir.project.structure.LLFirBuiltinsSessionFactory
-import org.jetbrains.kotlin.analysis.low.level.api.fir.services.KtCompilerPluginsProviderForTests
+import org.jetbrains.kotlin.analysis.low.level.api.fir.services.NoOpKtCompilerPluginsProvider
 import org.jetbrains.kotlin.analysis.low.level.api.fir.services.LLFirSealedClassInheritorsProcessorFactoryForTests
 import org.jetbrains.kotlin.analysis.low.level.api.fir.services.PackagePartProviderTestImpl
 import org.jetbrains.kotlin.analysis.low.level.api.fir.sessions.LLFirSessionCache
@@ -56,7 +56,7 @@ object AnalysisApiFirTestServiceRegistrar : AnalysisApiTestServiceRegistrar() {
             registerService(PackagePartProviderFactory::class.java, PackagePartProviderTestImpl(testServices))
 
             registerService(KotlinAsJavaSupport::class.java, SymbolKotlinAsJavaSupport(project))
-            registerService(KtCompilerPluginsProvider::class.java, KtCompilerPluginsProviderForTests(project))
+            registerService(KtCompilerPluginsProvider::class.java, NoOpKtCompilerPluginsProvider)
             registerService(ReadWriteAccessChecker::class.java, ReadWriteAccessCheckerFirImpl())
             registerService(KotlinReferenceProviderContributor::class.java, KotlinFirReferenceContributor::class.java)
         }
diff --git a/analysis/project-structure/src/org/jetbrains/kotlin/analysis/project/structure/KtCompilerPluginsProvider.kt b/analysis/project-structure/src/org/jetbrains/kotlin/analysis/project/structure/KtCompilerPluginsProvider.kt
index a453e25a8b3..4ec1ce8e684 100644
--- a/analysis/project-structure/src/org/jetbrains/kotlin/analysis/project/structure/KtCompilerPluginsProvider.kt
+++ b/analysis/project-structure/src/org/jetbrains/kotlin/analysis/project/structure/KtCompilerPluginsProvider.kt
@@ -13,6 +13,8 @@ import org.jetbrains.kotlin.extensions.ProjectExtensionDescriptor
 public abstract class KtCompilerPluginsProvider {
     /**
      * Returns a list of extensions of a base [extensionType] which are registered for [module]
+     *
+     * These extensions are used in addition to those provided by the extension descriptor's [ProjectExtensionDescriptor.getInstances].
      */
     public abstract fun <T : Any> getRegisteredExtensions(module: KtSourceModule, extensionType: ProjectExtensionDescriptor<T>): List<T>
 }