diff --git a/plugins/kotlin-serialization/kotlin-serialization-compiler/src/org/jetbrains/kotlinx/serialization/compiler/backend/ir/SerializableIrGenerator.kt b/plugins/kotlin-serialization/kotlin-serialization-compiler/src/org/jetbrains/kotlinx/serialization/compiler/backend/ir/SerializableIrGenerator.kt
index 84a3ba79baf..d31bf023e60 100644
--- a/plugins/kotlin-serialization/kotlin-serialization-compiler/src/org/jetbrains/kotlinx/serialization/compiler/backend/ir/SerializableIrGenerator.kt
+++ b/plugins/kotlin-serialization/kotlin-serialization-compiler/src/org/jetbrains/kotlinx/serialization/compiler/backend/ir/SerializableIrGenerator.kt
@@ -15,9 +15,7 @@ import org.jetbrains.kotlin.ir.builders.*
 import org.jetbrains.kotlin.ir.declarations.*
 import org.jetbrains.kotlin.ir.expressions.IrExpression
 import org.jetbrains.kotlin.ir.expressions.impl.IrDelegatingConstructorCallImpl
-import org.jetbrains.kotlin.ir.types.IrSimpleType
-import org.jetbrains.kotlin.ir.types.IrTypeProjection
-import org.jetbrains.kotlin.ir.types.classOrNull
+import org.jetbrains.kotlin.ir.types.*
 import org.jetbrains.kotlin.ir.util.getAnnotation
 import org.jetbrains.kotlin.ir.util.patchDeclarationParents
 import org.jetbrains.kotlin.js.resolve.diagnostics.findPsi
@@ -55,7 +53,8 @@ class SerializableIrGenerator(
 
             // Missing field exception parts
             val exceptionFqn = getSerializationPackageFqn(MISSING_FIELD_EXC)
-            val exceptionCtorRef = compilerContext.referenceConstructors(exceptionFqn).single { it.owner.isPrimary }
+            val exceptionCtorRef = compilerContext.referenceConstructors(exceptionFqn)
+                .single { it.owner.valueParameters.singleOrNull()?.type?.isString() == true }
             val exceptionType = exceptionCtorRef.owner.returnType
 
             val serializableProperties = properties.serializableProperties
diff --git a/plugins/kotlin-serialization/kotlin-serialization-compiler/src/org/jetbrains/kotlinx/serialization/compiler/backend/ir/SerializerIrGenerator.kt b/plugins/kotlin-serialization/kotlin-serialization-compiler/src/org/jetbrains/kotlinx/serialization/compiler/backend/ir/SerializerIrGenerator.kt
index 9e500c36ac5..83aa5c2c9aa 100644
--- a/plugins/kotlin-serialization/kotlin-serialization-compiler/src/org/jetbrains/kotlinx/serialization/compiler/backend/ir/SerializerIrGenerator.kt
+++ b/plugins/kotlin-serialization/kotlin-serialization-compiler/src/org/jetbrains/kotlinx/serialization/compiler/backend/ir/SerializerIrGenerator.kt
@@ -452,7 +452,8 @@ open class SerializerIrGenerator(val irClass: IrClass, final override val compil
                     // throw exception on unknown field
 
                     val exceptionFqn = getSerializationPackageFqn(UNKNOWN_FIELD_EXC)
-                    val excClassRef = compilerContext.referenceConstructors(exceptionFqn).single { it.owner.isPrimary }
+                    val excClassRef = compilerContext.referenceConstructors(exceptionFqn)
+                        .single { it.owner.valueParameters.singleOrNull()?.type?.isInt() == true }
                     +elseBranch(
                         irThrow(
                             irInvoke(