diff --git a/compiler/tests-common-new/tests/org/jetbrains/kotlin/test/frontend/classic/handlers/JspecifyDiagnosticComplianceHandler.kt b/compiler/tests-common-new/tests/org/jetbrains/kotlin/test/frontend/classic/handlers/JspecifyDiagnosticComplianceHandler.kt
index 86deb035b3f..4f52c7bec14 100644
--- a/compiler/tests-common-new/tests/org/jetbrains/kotlin/test/frontend/classic/handlers/JspecifyDiagnosticComplianceHandler.kt
+++ b/compiler/tests-common-new/tests/org/jetbrains/kotlin/test/frontend/classic/handlers/JspecifyDiagnosticComplianceHandler.kt
@@ -5,64 +5,89 @@
 
 package org.jetbrains.kotlin.test.frontend.classic.handlers
 
+import org.jetbrains.kotlin.codeMetaInfo.model.CodeMetaInfo
 import org.jetbrains.kotlin.codeMetaInfo.model.DiagnosticCodeMetaInfo
 import org.jetbrains.kotlin.codeMetaInfo.model.JspecifyMarkerCodeMetaInfo
 import org.jetbrains.kotlin.diagnostics.Errors
+import org.jetbrains.kotlin.fir.analysis.diagnostics.FirErrors
 import org.jetbrains.kotlin.load.java.JSPECIFY_ANNOTATIONS_PACKAGE
 import org.jetbrains.kotlin.load.java.ReportLevel
 import org.jetbrains.kotlin.load.java.getDefaultReportLevelForAnnotation
 import org.jetbrains.kotlin.resolve.jvm.diagnostics.ErrorsJvm
 import org.jetbrains.kotlin.test.directives.ForeignAnnotationsDirectives
 import org.jetbrains.kotlin.test.frontend.classic.ClassicFrontendOutputArtifact
+import org.jetbrains.kotlin.test.frontend.fir.FirOutputArtifact
+import org.jetbrains.kotlin.test.frontend.fir.handlers.FirAnalysisHandler
+import org.jetbrains.kotlin.test.frontend.fir.handlers.FirDiagnosticCodeMetaInfo
+import org.jetbrains.kotlin.test.model.TestFile
 import org.jetbrains.kotlin.test.model.TestModule
 import org.jetbrains.kotlin.test.services.TestServices
 import org.jetbrains.kotlin.test.services.globalMetadataInfoHandler
+import org.jetbrains.kotlin.test.services.sourceFileProvider
 
-// Not that this diagnostic handler should be included only with `ClassicDiagnosticsHandler` and go after it
-class JspecifyDiagnosticComplianceHandler(testServices: TestServices) : ClassicFrontendAnalysisHandler(testServices) {
-    override fun processModule(module: TestModule, info: ClassicFrontendOutputArtifact) {
-        val jspecifyMode = module.directives[ForeignAnnotationsDirectives.JSPECIFY_STATE].singleOrNull()
-            ?: getDefaultReportLevelForAnnotation(JSPECIFY_ANNOTATIONS_PACKAGE)
+private fun TestServices.generateJspecifyMetadataInfos(
+    module: TestModule, files: Iterable<TestFile>, diagnosticKind: (CodeMetaInfo) -> Any?
+) {
+    val jspecifyMode = module.directives[ForeignAnnotationsDirectives.JSPECIFY_STATE].singleOrNull()
+        ?: getDefaultReportLevelForAnnotation(JSPECIFY_ANNOTATIONS_PACKAGE)
+    val diagnosticsToJspecifyMarksForMode = diagnosticsToJspecifyMarks[jspecifyMode] ?: return
 
-        for ((testFile, ktFile) in info.allKtFiles) {
-            val reportedDiagnostics =
-                testServices.globalMetadataInfoHandler.getReportedMetaInfosForFile(testFile).filterIsInstance<DiagnosticCodeMetaInfo>()
-            for (metaInfo in reportedDiagnostics) {
-                val jspecifyMark = diagnosticsToJspecifyMarks.getValue(jspecifyMode)[metaInfo.diagnostic.factory] ?: continue
-                val fileLines = ktFile.text.lines()
-                val fileLinePositions =
-                    fileLines.map { it.length }.runningReduce { sumLength, length -> sumLength + length + 1 }
-                val lineIndexToPasteJspecifyMark = fileLinePositions.indexOfLast { it < metaInfo.start }
-                val positionToPasteJspecifyMark = fileLinePositions[lineIndexToPasteJspecifyMark]
-                val offset = fileLines[lineIndexToPasteJspecifyMark + 1].takeWhile { it == ' ' }.length
-
-                testServices.globalMetadataInfoHandler.addMetadataInfosForFile(
-                    testFile,
-                    listOf(JspecifyMarkerCodeMetaInfo(positionToPasteJspecifyMark, positionToPasteJspecifyMark, offset, jspecifyMark))
-                )
-            }
+    for (testFile in files) {
+        val fileLines = sourceFileProvider.getContentOfSourceFile(testFile).lines()
+        val fileLinePositions =
+            fileLines.map { it.length }.runningReduce { sumLength, length -> sumLength + length + 1 }
+        val newMetaInfos = globalMetadataInfoHandler.getReportedMetaInfosForFile(testFile).mapNotNull { metaInfo ->
+            val diagnostic = diagnosticKind(metaInfo) ?: return@mapNotNull null
+            val jspecifyMark = diagnosticsToJspecifyMarksForMode[diagnostic] ?: return@mapNotNull null
+            val lineIndexToPasteJspecifyMark = fileLinePositions.indexOfLast { it < metaInfo.start }
+            val positionToPasteJspecifyMark = fileLinePositions[lineIndexToPasteJspecifyMark]
+            val offset = fileLines[lineIndexToPasteJspecifyMark + 1].takeWhile { it == ' ' }.length
+            JspecifyMarkerCodeMetaInfo(positionToPasteJspecifyMark, positionToPasteJspecifyMark, offset, jspecifyMark)
         }
+        globalMetadataInfoHandler.addMetadataInfosForFile(testFile, newMetaInfos)
     }
+}
+
+internal val diagnosticsToJspecifyMarks = mapOf(
+    ReportLevel.WARN to mapOf(
+        ErrorsJvm.NULLABILITY_MISMATCH_BASED_ON_JAVA_ANNOTATIONS to "jspecify_nullness_mismatch",
+        ErrorsJvm.UPPER_BOUND_VIOLATED_BASED_ON_JAVA_ANNOTATIONS to "jspecify_nullness_mismatch",
+        ErrorsJvm.NULLABILITY_MISMATCH_BASED_ON_JAVA_ANNOTATIONS to "jspecify_nullness_mismatch",
+        ErrorsJvm.RECEIVER_NULLABILITY_MISMATCH_BASED_ON_JAVA_ANNOTATIONS to "jspecify_nullness_mismatch",
+        // TODO: list FIR warnings (they don't exist yet)
+    ),
+    ReportLevel.STRICT to mapOf(
+        Errors.TYPE_MISMATCH to "jspecify_nullness_mismatch",
+        Errors.NULL_FOR_NONNULL_TYPE to "jspecify_nullness_mismatch",
+        Errors.NOTHING_TO_OVERRIDE to "jspecify_nullness_mismatch",
+        Errors.RETURN_TYPE_MISMATCH_ON_OVERRIDE to "jspecify_nullness_mismatch",
+        Errors.UPPER_BOUND_VIOLATED to "jspecify_nullness_mismatch",
+        Errors.UNSAFE_CALL to "jspecify_nullness_mismatch",
+
+        FirErrors.ARGUMENT_TYPE_MISMATCH to "jspecify_nullness_mismatch",
+        FirErrors.NULL_FOR_NONNULL_TYPE to "jspecify_nullness_mismatch",
+        FirErrors.NOTHING_TO_OVERRIDE to "jspecify_nullness_mismatch",
+        FirErrors.RETURN_TYPE_MISMATCH_ON_OVERRIDE to "jspecify_nullness_mismatch",
+        FirErrors.UPPER_BOUND_VIOLATED to "jspecify_nullness_mismatch",
+        FirErrors.UNSAFE_CALL to "jspecify_nullness_mismatch",
+    ),
+    ReportLevel.IGNORE to emptyMap()
+)
+
+class JspecifyDiagnosticComplianceHandler(testServices: TestServices) : ClassicFrontendAnalysisHandler(testServices) {
+    override fun processModule(module: TestModule, info: ClassicFrontendOutputArtifact) =
+        testServices.generateJspecifyMetadataInfos(module, info.allKtFiles.keys) {
+            (it as? DiagnosticCodeMetaInfo)?.diagnostic?.factory
+        }
 
     override fun processAfterAllModules(someAssertionWasFailed: Boolean) {}
+}
 
-    companion object {
-        val diagnosticsToJspecifyMarks = mapOf(
-            ReportLevel.WARN to mapOf(
-                ErrorsJvm.NULLABILITY_MISMATCH_BASED_ON_JAVA_ANNOTATIONS to "jspecify_nullness_mismatch",
-                ErrorsJvm.UPPER_BOUND_VIOLATED_BASED_ON_JAVA_ANNOTATIONS to "jspecify_nullness_mismatch",
-                ErrorsJvm.NULLABILITY_MISMATCH_BASED_ON_JAVA_ANNOTATIONS to "jspecify_nullness_mismatch",
-                ErrorsJvm.RECEIVER_NULLABILITY_MISMATCH_BASED_ON_JAVA_ANNOTATIONS to "jspecify_nullness_mismatch",
-            ),
-            ReportLevel.STRICT to mapOf(
-                Errors.TYPE_MISMATCH to "jspecify_nullness_mismatch",
-                Errors.NULL_FOR_NONNULL_TYPE to "jspecify_nullness_mismatch",
-                Errors.NOTHING_TO_OVERRIDE to "jspecify_nullness_mismatch",
-                Errors.RETURN_TYPE_MISMATCH_ON_OVERRIDE to "jspecify_nullness_mismatch",
-                Errors.UPPER_BOUND_VIOLATED to "jspecify_nullness_mismatch",
-                Errors.UNSAFE_CALL to "jspecify_nullness_mismatch",
-            ),
-            ReportLevel.IGNORE to emptyMap()
-        )
-    }
-}
\ No newline at end of file
+class FirJspecifyDiagnosticComplianceHandler(testServices: TestServices) : FirAnalysisHandler(testServices) {
+    override fun processModule(module: TestModule, info: FirOutputArtifact) =
+        testServices.generateJspecifyMetadataInfos(module, info.allFirFiles.keys) {
+            (it as? FirDiagnosticCodeMetaInfo)?.diagnostic?.factory
+        }
+
+    override fun processAfterAllModules(someAssertionWasFailed: Boolean) {}
+}
diff --git a/compiler/tests-common-new/tests/org/jetbrains/kotlin/test/preprocessors/JspecifyMarksCleanupPreprocessor.kt b/compiler/tests-common-new/tests/org/jetbrains/kotlin/test/preprocessors/JspecifyMarksCleanupPreprocessor.kt
index bea2319d1ab..c47c413dbca 100644
--- a/compiler/tests-common-new/tests/org/jetbrains/kotlin/test/preprocessors/JspecifyMarksCleanupPreprocessor.kt
+++ b/compiler/tests-common-new/tests/org/jetbrains/kotlin/test/preprocessors/JspecifyMarksCleanupPreprocessor.kt
@@ -5,7 +5,7 @@
 
 package org.jetbrains.kotlin.test.preprocessors
 
-import org.jetbrains.kotlin.test.frontend.classic.handlers.JspecifyDiagnosticComplianceHandler.Companion.diagnosticsToJspecifyMarks
+import org.jetbrains.kotlin.test.frontend.classic.handlers.diagnosticsToJspecifyMarks
 import org.jetbrains.kotlin.test.model.TestFile
 import org.jetbrains.kotlin.test.services.*