diff --git a/plugins/kotlinx-serialization/kotlinx-serialization.backend/src/org/jetbrains/kotlinx/serialization/compiler/backend/ir/SerializableCompanionIrGenerator.kt b/plugins/kotlinx-serialization/kotlinx-serialization.backend/src/org/jetbrains/kotlinx/serialization/compiler/backend/ir/SerializableCompanionIrGenerator.kt
index 7d15195bfe4..b780031f1a3 100644
--- a/plugins/kotlinx-serialization/kotlinx-serialization.backend/src/org/jetbrains/kotlinx/serialization/compiler/backend/ir/SerializableCompanionIrGenerator.kt
+++ b/plugins/kotlinx-serialization/kotlinx-serialization.backend/src/org/jetbrains/kotlinx/serialization/compiler/backend/ir/SerializableCompanionIrGenerator.kt
@@ -35,10 +35,13 @@ class SerializableCompanionIrGenerator(
 
     companion object {
         fun getSerializerGetterFunction(serializableIrClass: IrClass): IrSimpleFunction? {
-            val irClass = if (serializableIrClass.isSerializableObject) serializableIrClass else serializableIrClass.companionObject() ?: return null
+            val irClass =
+                if (serializableIrClass.isSerializableObject) serializableIrClass else serializableIrClass.companionObject() ?: return null
             return irClass.findDeclaration<IrSimpleFunction> {
-                (it.valueParameters.size == serializableIrClass.typeParameters.size
-                        && it.valueParameters.all { p -> p.type.isKSerializer() }) && it.returnType.isKSerializer()
+                it.name == SerialEntityNames.SERIALIZER_PROVIDER_NAME
+                        && it.valueParameters.size == serializableIrClass.typeParameters.size
+                        && it.valueParameters.all { p -> p.type.isKSerializer() }
+                        && it.returnType.isKSerializer()
             }
         }
 
@@ -57,10 +60,12 @@ class SerializableCompanionIrGenerator(
     }
 
     fun generate() {
-        val serializerGetterFunction = getSerializerGetterFunction(serializableIrClass) ?: throw IllegalStateException(
-            "Can't find synthesized 'Companion.serializer()' function to generate, " +
-                    "probably clash with user-defined function has occurred"
-        )
+        val serializerGetterFunction =
+            getSerializerGetterFunction(serializableIrClass)?.takeIf { it.isFromPlugin(compilerContext.afterK2) }
+                ?: throw IllegalStateException(
+                    "Can't find synthesized 'Companion.serializer()' function to generate, " +
+                            "probably clash with user-defined function has occurred"
+                )
 
         if (serializableIrClass.isSerializableObject
             || serializableIrClass.isAbstractOrSealedSerializableClass
@@ -115,7 +120,8 @@ class SerializableCompanionIrGenerator(
             )
         )
 
-        val kSerializerIrClass = compilerContext.referenceClass(ClassId(SerializationPackages.packageFqName, SerialEntityNames.KSERIALIZER_NAME))!!.owner
+        val kSerializerIrClass =
+            compilerContext.referenceClass(ClassId(SerializationPackages.packageFqName, SerialEntityNames.KSERIALIZER_NAME))!!.owner
         val targetIrType =
             kSerializerIrClass.defaultType.substitute(mapOf(kSerializerIrClass.typeParameters[0].symbol to compilerContext.irBuiltIns.anyType))
 
@@ -154,7 +160,8 @@ class SerializableCompanionIrGenerator(
 
     private fun getOrCreateSerializerVarargFactory(): IrSimpleFunction {
         irClass.findDeclaration<IrSimpleFunction> {
-            it.valueParameters.size == 1
+            it.name == SerialEntityNames.SERIALIZER_PROVIDER_NAME
+                    && it.valueParameters.size == 1
                     && it.valueParameters.first().isVararg
                     && it.returnType.isKSerializer()
                     && it.isFromPlugin(compilerContext.afterK2)
diff --git a/plugins/kotlinx-serialization/testData/boxIr/userDefinedSerializerInCompanion.kt b/plugins/kotlinx-serialization/testData/boxIr/userDefinedSerializerInCompanion.kt
new file mode 100644
index 00000000000..d6a3532d7bb
--- /dev/null
+++ b/plugins/kotlinx-serialization/testData/boxIr/userDefinedSerializerInCompanion.kt
@@ -0,0 +1,37 @@
+// TARGET_BACKEND: JVM_IR
+
+// WITH_STDLIB
+
+import kotlinx.serialization.*
+import kotlinx.serialization.descriptors.*
+import kotlinx.serialization.builtins.*
+
+
+@Serializable
+data class Main(val fields: MainFields) {
+    companion object  {
+        fun fieldsSerializer(): KSerializer<MainFields> = MainFields.serializer()
+    }
+}
+
+@Serializable
+data class MainFields(val firstName: String?)
+
+@Serializable
+data class Box<T>(val boxed: T) {
+    companion object {
+        fun <T> serializerLike(tSer: KSerializer<T>): KSerializer<List<Box<T>>> = ListSerializer(serializer(tSer))
+    }
+}
+
+
+fun box(): String {
+    if (Main.fieldsSerializer().descriptor.toString() != "MainFields(firstName: kotlin.String?)") return "Error1"
+    if (MainFields.serializer().descriptor.toString() != "MainFields(firstName: kotlin.String?)") return "Error2"
+    if (Main.serializer().descriptor.toString() != "Main(fields: MainFields)") return "Error3"
+    val boxListDesc = Box.serializerLike(String.serializer()).descriptor
+    if (boxListDesc.toString() != "kotlin.collections.ArrayList(Box(boxed: kotlin.String))") return boxListDesc.toString()
+    val boxDesc = Box.serializer(String.serializer()).descriptor
+    if (boxDesc.toString() != "Box(boxed: kotlin.String)") return boxDesc.toString()
+    return "OK"
+}
\ No newline at end of file
diff --git a/plugins/kotlinx-serialization/tests-gen/org/jetbrains/kotlinx/serialization/runners/SerializationFirBlackBoxTestGenerated.java b/plugins/kotlinx-serialization/tests-gen/org/jetbrains/kotlinx/serialization/runners/SerializationFirBlackBoxTestGenerated.java
index 0eb5e4d47f8..b0db2c69dbe 100644
--- a/plugins/kotlinx-serialization/tests-gen/org/jetbrains/kotlinx/serialization/runners/SerializationFirBlackBoxTestGenerated.java
+++ b/plugins/kotlinx-serialization/tests-gen/org/jetbrains/kotlinx/serialization/runners/SerializationFirBlackBoxTestGenerated.java
@@ -158,6 +158,12 @@ public class SerializationFirBlackBoxTestGenerated extends AbstractSerialization
         public void testUseSerializersChain() throws Exception {
             runTest("plugins/kotlinx-serialization/testData/boxIr/useSerializersChain.kt");
         }
+
+        @Test
+        @TestMetadata("userDefinedSerializerInCompanion.kt")
+        public void testUserDefinedSerializerInCompanion() throws Exception {
+            runTest("plugins/kotlinx-serialization/testData/boxIr/userDefinedSerializerInCompanion.kt");
+        }
     }
 
     @Nested
diff --git a/plugins/kotlinx-serialization/tests-gen/org/jetbrains/kotlinx/serialization/runners/SerializationIrBoxTestGenerated.java b/plugins/kotlinx-serialization/tests-gen/org/jetbrains/kotlinx/serialization/runners/SerializationIrBoxTestGenerated.java
index 50a26920d25..f8d70a3ea86 100644
--- a/plugins/kotlinx-serialization/tests-gen/org/jetbrains/kotlinx/serialization/runners/SerializationIrBoxTestGenerated.java
+++ b/plugins/kotlinx-serialization/tests-gen/org/jetbrains/kotlinx/serialization/runners/SerializationIrBoxTestGenerated.java
@@ -156,4 +156,10 @@ public class SerializationIrBoxTestGenerated extends AbstractSerializationIrBoxT
     public void testUseSerializersChain() throws Exception {
         runTest("plugins/kotlinx-serialization/testData/boxIr/useSerializersChain.kt");
     }
+
+    @Test
+    @TestMetadata("userDefinedSerializerInCompanion.kt")
+    public void testUserDefinedSerializerInCompanion() throws Exception {
+        runTest("plugins/kotlinx-serialization/testData/boxIr/userDefinedSerializerInCompanion.kt");
+    }
 }