diff --git a/compiler/fir/checkers/src/org/jetbrains/kotlin/fir/analysis/checkers/expression/FirOptInUsageBaseChecker.kt b/compiler/fir/checkers/src/org/jetbrains/kotlin/fir/analysis/checkers/expression/FirOptInUsageBaseChecker.kt
index d827b67449f..92af4640d5b 100644
--- a/compiler/fir/checkers/src/org/jetbrains/kotlin/fir/analysis/checkers/expression/FirOptInUsageBaseChecker.kt
+++ b/compiler/fir/checkers/src/org/jetbrains/kotlin/fir/analysis/checkers/expression/FirOptInUsageBaseChecker.kt
@@ -110,7 +110,8 @@ object FirOptInUsageBaseChecker {
                 }
             }
             if (fir !is FirConstructor) {
-                fir.returnTypeRef.coneType.addExperimentalities(context, result, visited)
+                // Without coneTypeSafe v fails in MT test (FirRenderer.kt)
+                fir.returnTypeRef.coneTypeSafe<ConeKotlinType>().addExperimentalities(context, result, visited)
                 fir.receiverTypeRef?.coneType.addExperimentalities(context, result, visited)
                 if (fir is FirSimpleFunction) {
                     fir.valueParameters.forEach {