diff --git a/compiler/ir/serialization.common/src/org/jetbrains/kotlin/backend/common/serialization/IrFileSerializer.kt b/compiler/ir/serialization.common/src/org/jetbrains/kotlin/backend/common/serialization/IrFileSerializer.kt
index 785691ccc44..10bceceb0af 100644
--- a/compiler/ir/serialization.common/src/org/jetbrains/kotlin/backend/common/serialization/IrFileSerializer.kt
+++ b/compiler/ir/serialization.common/src/org/jetbrains/kotlin/backend/common/serialization/IrFileSerializer.kt
@@ -1063,7 +1063,7 @@ open class IrFileSerializer(
         expression.label?.let {
             proto.label = serializeString(it)
         }
-        val loopId = loopIndex[expression.loop]!!
+        val loopId = loopIndex[expression.loop] ?: -1
         proto.loopId = loopId
 
         return proto.build()