diff --git a/analysis/decompiled/decompiler-to-file-stubs/src/org/jetbrains/kotlin/analysis/decompiler/stub/file/KotlinMetadataStubBuilder.kt b/analysis/decompiled/decompiler-to-file-stubs/src/org/jetbrains/kotlin/analysis/decompiler/stub/file/KotlinMetadataStubBuilder.kt
index 059c25ab50f..91d683f2295 100644
--- a/analysis/decompiled/decompiler-to-file-stubs/src/org/jetbrains/kotlin/analysis/decompiler/stub/file/KotlinMetadataStubBuilder.kt
+++ b/analysis/decompiled/decompiler-to-file-stubs/src/org/jetbrains/kotlin/analysis/decompiler/stub/file/KotlinMetadataStubBuilder.kt
@@ -33,7 +33,7 @@ open class KotlinMetadataStubBuilder(
 
     override fun buildFileStub(content: FileContent): PsiFileStub<*>? {
         val virtualFile = content.file
-        assert(virtualFile.fileType == fileType) { "Unexpected file type ${virtualFile.fileType}" }
+        assert(virtualFile.extension == fileType.defaultExtension || virtualFile.fileType == fileType) { "Unexpected file type ${virtualFile.fileType.name}" }
         val file = readFile(virtualFile, content.content) ?: return null
 
         when (file) {
diff --git a/analysis/decompiled/decompiler-to-psi/src/org/jetbrains/kotlin/analysis/decompiler/psi/KotlinMetadataDecompiler.kt b/analysis/decompiled/decompiler-to-psi/src/org/jetbrains/kotlin/analysis/decompiler/psi/KotlinMetadataDecompiler.kt
index 84579ec686c..7c1e89d0d6d 100644
--- a/analysis/decompiled/decompiler-to-psi/src/org/jetbrains/kotlin/analysis/decompiler/psi/KotlinMetadataDecompiler.kt
+++ b/analysis/decompiled/decompiler-to-psi/src/org/jetbrains/kotlin/analysis/decompiler/psi/KotlinMetadataDecompiler.kt
@@ -40,7 +40,7 @@ abstract class KotlinMetadataDecompiler<out V : BinaryVersion>(
 
     abstract fun readFile(bytes: ByteArray, file: VirtualFile): KotlinMetadataStubBuilder.FileWithMetadata?
 
-    override fun accepts(file: VirtualFile) = file.fileType == fileType
+    override fun accepts(file: VirtualFile) = file.extension == fileType.defaultExtension || file.fileType == fileType
 
     override fun getStubBuilder() = metadataStubBuilder
 
diff --git a/analysis/decompiled/light-classes-for-decompiled/src/org/jetbrains/kotlin/analysis/decompiled/light/classes/ClsJavaStubByVirtualFileCache.kt b/analysis/decompiled/light-classes-for-decompiled/src/org/jetbrains/kotlin/analysis/decompiled/light/classes/ClsJavaStubByVirtualFileCache.kt
index c1187e0aa68..fd4d43fe806 100644
--- a/analysis/decompiled/light-classes-for-decompiled/src/org/jetbrains/kotlin/analysis/decompiled/light/classes/ClsJavaStubByVirtualFileCache.kt
+++ b/analysis/decompiled/light-classes-for-decompiled/src/org/jetbrains/kotlin/analysis/decompiled/light/classes/ClsJavaStubByVirtualFileCache.kt
@@ -33,7 +33,7 @@ class ClsJavaStubByVirtualFileCache {
     }
 
     private fun createStub(file: VirtualFile): PsiJavaFileStub? {
-        if (file.fileType !== JavaClassFileType.INSTANCE) return null
+        if (file.extension != JavaClassFileType.INSTANCE.defaultExtension && file.fileType !== JavaClassFileType.INSTANCE) return null
 
         try {
             return ClsFileImpl.buildFileStub(file, file.contentsToByteArray(false))
diff --git a/compiler/cli/src/org/jetbrains/kotlin/cli/jvm/compiler/KotlinCoreEnvironment.kt b/compiler/cli/src/org/jetbrains/kotlin/cli/jvm/compiler/KotlinCoreEnvironment.kt
index cb1a23dab4b..faa363c4b33 100644
--- a/compiler/cli/src/org/jetbrains/kotlin/cli/jvm/compiler/KotlinCoreEnvironment.kt
+++ b/compiler/cli/src/org/jetbrains/kotlin/cli/jvm/compiler/KotlinCoreEnvironment.kt
@@ -314,7 +314,7 @@ class KotlinCoreEnvironment private constructor(
     private val VirtualFile.javaFiles: List<VirtualFile>
         get() = mutableListOf<VirtualFile>().apply {
             VfsUtilCore.processFilesRecursively(this@javaFiles) { file ->
-                if (file.fileType == JavaFileType.INSTANCE) {
+                if (file.extension == JavaFileType.DEFAULT_EXTENSION || file.fileType == JavaFileType.INSTANCE) {
                     add(file)
                 }
                 true
diff --git a/compiler/cli/src/org/jetbrains/kotlin/cli/jvm/compiler/TopDownAnalyzerFacadeForJVM.kt b/compiler/cli/src/org/jetbrains/kotlin/cli/jvm/compiler/TopDownAnalyzerFacadeForJVM.kt
index 837bd310abd..65ef320a425 100644
--- a/compiler/cli/src/org/jetbrains/kotlin/cli/jvm/compiler/TopDownAnalyzerFacadeForJVM.kt
+++ b/compiler/cli/src/org/jetbrains/kotlin/cli/jvm/compiler/TopDownAnalyzerFacadeForJVM.kt
@@ -310,7 +310,7 @@ object TopDownAnalyzerFacadeForJVM {
         // 'isDirectory' check is needed because otherwise directories such as 'frontend.java' would be recognized
         // as Java source files, which makes no sense
         override fun contains(file: VirtualFile) =
-            file.fileType === JavaFileType.INSTANCE && !file.isDirectory
+            (file.extension == JavaFileType.DEFAULT_EXTENSION || file.fileType === JavaFileType.INSTANCE) && !file.isDirectory
 
         override fun toString() = "All Java sources in the project"
     }
diff --git a/compiler/cli/src/org/jetbrains/kotlin/cli/jvm/compiler/coreEnvironmentUtils.kt b/compiler/cli/src/org/jetbrains/kotlin/cli/jvm/compiler/coreEnvironmentUtils.kt
index 61d8d05bfc7..fb121b95eda 100644
--- a/compiler/cli/src/org/jetbrains/kotlin/cli/jvm/compiler/coreEnvironmentUtils.kt
+++ b/compiler/cli/src/org/jetbrains/kotlin/cli/jvm/compiler/coreEnvironmentUtils.kt
@@ -58,7 +58,7 @@ inline fun List<KotlinSourceRoot>.forAllFiles(
             continue
         }
 
-        if (!vFile.isDirectory && vFile.fileType != KotlinFileType.INSTANCE) {
+        if (!vFile.isDirectory && vFile.extension != KotlinFileType.EXTENSION && vFile.fileType != KotlinFileType.INSTANCE) {
             configuration.report(CompilerMessageSeverity.ERROR, "Source entry is not a Kotlin file: $sourceRootPath", reportLocation)
             continue
         }
diff --git a/compiler/frontend.common.jvm/src/org/jetbrains/kotlin/load/kotlin/KotlinBinaryClassCache.kt b/compiler/frontend.common.jvm/src/org/jetbrains/kotlin/load/kotlin/KotlinBinaryClassCache.kt
index f71242fd2c3..b1b4d835478 100644
--- a/compiler/frontend.common.jvm/src/org/jetbrains/kotlin/load/kotlin/KotlinBinaryClassCache.kt
+++ b/compiler/frontend.common.jvm/src/org/jetbrains/kotlin/load/kotlin/KotlinBinaryClassCache.kt
@@ -62,7 +62,9 @@ class KotlinBinaryClassCache : Disposable {
         fun getKotlinBinaryClassOrClassFileContent(
             file: VirtualFile, fileContent: ByteArray? = null
         ): KotlinClassFinder.Result? {
-            if (file.fileType !== JavaClassFileType.INSTANCE) return null
+            if (file.extension != JavaClassFileType.INSTANCE.defaultExtension &&
+                file.fileType !== JavaClassFileType.INSTANCE
+            ) return null
 
             if (file.name == PsiJavaModule.MODULE_INFO_CLS_FILE) return null
 
diff --git a/compiler/frontend.common.jvm/src/org/jetbrains/kotlin/load/kotlin/VirtualFileKotlinClass.kt b/compiler/frontend.common.jvm/src/org/jetbrains/kotlin/load/kotlin/VirtualFileKotlinClass.kt
index 903bded0252..5c568fb885f 100644
--- a/compiler/frontend.common.jvm/src/org/jetbrains/kotlin/load/kotlin/VirtualFileKotlinClass.kt
+++ b/compiler/frontend.common.jvm/src/org/jetbrains/kotlin/load/kotlin/VirtualFileKotlinClass.kt
@@ -9,7 +9,6 @@ import com.intellij.ide.highlighter.JavaClassFileType
 import com.intellij.openapi.diagnostic.ControlFlowException
 import com.intellij.openapi.diagnostic.Logger
 import com.intellij.openapi.vfs.VirtualFile
-import org.jetbrains.kotlin.load.kotlin.KotlinClassFinder
 import org.jetbrains.kotlin.load.kotlin.KotlinClassFinder.Result.KotlinClass
 import org.jetbrains.kotlin.load.kotlin.header.KotlinClassHeader
 import org.jetbrains.kotlin.name.ClassId
@@ -49,7 +48,7 @@ class VirtualFileKotlinClass private constructor(
 
         internal fun create(file: VirtualFile, fileContent: ByteArray?): KotlinClassFinder.Result? {
             return perfCounter.time {
-                assert(file.fileType == JavaClassFileType.INSTANCE) { "Trying to read binary data from a non-class file $file" }
+                assert(file.extension == JavaClassFileType.INSTANCE.defaultExtension || file.fileType == JavaClassFileType.INSTANCE) { "Trying to read binary data from a non-class file $file" }
 
                 try {
                     val byteContent = fileContent ?: file.contentsToByteArray(false)
diff --git a/compiler/frontend.java/src/org/jetbrains/kotlin/resolve/jvm/modules/JavaModule.kt b/compiler/frontend.java/src/org/jetbrains/kotlin/resolve/jvm/modules/JavaModule.kt
index 29d4c19a0e6..6e0f3cdebd7 100644
--- a/compiler/frontend.java/src/org/jetbrains/kotlin/resolve/jvm/modules/JavaModule.kt
+++ b/compiler/frontend.java/src/org/jetbrains/kotlin/resolve/jvm/modules/JavaModule.kt
@@ -90,7 +90,7 @@ interface JavaModule {
             get() = moduleInfo.moduleName
 
         override val isSourceModule: Boolean
-            get() = moduleInfoFile.fileType == JavaFileType.INSTANCE
+            get() = moduleInfoFile.extension == JavaFileType.DEFAULT_EXTENSION || moduleInfoFile.fileType == JavaFileType.INSTANCE
 
         override fun exports(packageFqName: FqName): Boolean {
             return moduleInfo.exports.any { (fqName, toModules) ->
diff --git a/plugins/scripting/scripting-compiler-impl/src/org/jetbrains/kotlin/scripting/resolve/refineCompilationConfiguration.kt b/plugins/scripting/scripting-compiler-impl/src/org/jetbrains/kotlin/scripting/resolve/refineCompilationConfiguration.kt
index 0b600868076..99dfe8528f8 100644
--- a/plugins/scripting/scripting-compiler-impl/src/org/jetbrains/kotlin/scripting/resolve/refineCompilationConfiguration.kt
+++ b/plugins/scripting/scripting-compiler-impl/src/org/jetbrains/kotlin/scripting/resolve/refineCompilationConfiguration.kt
@@ -55,7 +55,7 @@ internal fun VirtualFile.getAnnotationEntries(project: Project): Iterable<KtAnno
     val psiFile: PsiFile = PsiManager.getInstance(project).findFile(this)
         ?: throw IllegalArgumentException("Unable to load PSI from $canonicalPath")
     return (psiFile as? KtFile)?.annotationEntries
-        ?: throw IllegalArgumentException("Unable to extract kotlin annotations from $name ($fileType)")
+        ?: throw IllegalArgumentException("Unable to extract kotlin annotations from $name (${fileType.name})")
 }
 
 /**
@@ -335,7 +335,7 @@ fun SourceCode.getKtFile(definition: ScriptDefinition, project: Project): KtFile
             val psiFile: PsiFile = PsiManager.getInstance(project).findFile(file)
                 ?: throw IllegalArgumentException("Unable to load PSI from ${file.path}")
             (psiFile as? KtFile)
-                ?: throw IllegalArgumentException("Not a kotlin file ${file.path} (${file.fileType})")
+                ?: throw IllegalArgumentException("Not a kotlin file ${file.path} (${file.fileType.name})")
         }
     }