diff --git a/plugins/kotlinx-serialization/kotlinx-serialization.k2/src/org/jetbrains/kotlinx/serialization/compiler/fir/SerializationFirResolveExtension.kt b/plugins/kotlinx-serialization/kotlinx-serialization.k2/src/org/jetbrains/kotlinx/serialization/compiler/fir/SerializationFirResolveExtension.kt
index 9974a68d8ab..d5a6fa5dc88 100644
--- a/plugins/kotlinx-serialization/kotlinx-serialization.k2/src/org/jetbrains/kotlinx/serialization/compiler/fir/SerializationFirResolveExtension.kt
+++ b/plugins/kotlinx-serialization/kotlinx-serialization.k2/src/org/jetbrains/kotlinx/serialization/compiler/fir/SerializationFirResolveExtension.kt
@@ -11,10 +11,8 @@ import org.jetbrains.kotlin.descriptors.Visibilities
 import org.jetbrains.kotlin.fir.FirSession
 import org.jetbrains.kotlin.fir.containingClassForStaticMemberAttr
 import org.jetbrains.kotlin.fir.copy
-import org.jetbrains.kotlin.fir.declarations.FirDeclarationOrigin
-import org.jetbrains.kotlin.fir.declarations.FirSimpleFunction
+import org.jetbrains.kotlin.fir.declarations.*
 import org.jetbrains.kotlin.fir.declarations.builder.buildSimpleFunctionCopy
-import org.jetbrains.kotlin.fir.declarations.origin
 import org.jetbrains.kotlin.fir.declarations.utils.isCompanion
 import org.jetbrains.kotlin.fir.extensions.*
 import org.jetbrains.kotlin.fir.plugin.*
@@ -278,6 +276,8 @@ class SerializationFirResolveExtension(session: FirSession) : FirDeclarationGene
         val hasTypeParams = owner.typeParameterSymbols.isNotEmpty()
         val serializerKind = if (hasTypeParams) ClassKind.CLASS else ClassKind.OBJECT
         val serializerFirClass = createNestedClass(owner, SerialEntityNames.SERIALIZER_CLASS_NAME, SerializationPluginKey, serializerKind) {
+            modality = Modality.FINAL
+
             for (parameter in owner.typeParameterSymbols) {
                 typeParameter(parameter.name)
             }
@@ -292,11 +292,10 @@ class SerializationFirResolveExtension(session: FirSession) : FirDeclarationGene
                     isNullable = false
                 )
             }
+        }.apply {
+            excludeFromJsExport()
+            markAsDeprecatedHidden()
         }
-        // TODO: add deprecate hidden
-        // serializerFirClass.replaceAnnotations(listOf(Annotations.create(listOf(KSerializerDescriptorResolver.createDeprecatedHiddenAnnotation(thisDescriptor.module)))))
-        serializerFirClass.excludeFromJsExport()
-
         return serializerFirClass.symbol
     }
 
diff --git a/plugins/kotlinx-serialization/kotlinx-serialization.k2/src/org/jetbrains/kotlinx/serialization/compiler/fir/SerializationFirUtils.kt b/plugins/kotlinx-serialization/kotlinx-serialization.k2/src/org/jetbrains/kotlinx/serialization/compiler/fir/SerializationFirUtils.kt
index 160585baea6..ff5f9c7da4e 100644
--- a/plugins/kotlinx-serialization/kotlinx-serialization.k2/src/org/jetbrains/kotlinx/serialization/compiler/fir/SerializationFirUtils.kt
+++ b/plugins/kotlinx-serialization/kotlinx-serialization.k2/src/org/jetbrains/kotlinx/serialization/compiler/fir/SerializationFirUtils.kt
@@ -8,8 +8,9 @@ package org.jetbrains.kotlinx.serialization.compiler.fir
 import org.jetbrains.kotlin.descriptors.*
 import org.jetbrains.kotlin.fir.FirSession
 import org.jetbrains.kotlin.fir.declarations.*
+import org.jetbrains.kotlin.fir.deserialization.toQualifiedPropertyAccessExpression
 import org.jetbrains.kotlin.fir.expressions.*
-import org.jetbrains.kotlin.fir.expressions.builder.buildAnnotationCall
+import org.jetbrains.kotlin.fir.expressions.builder.*
 import org.jetbrains.kotlin.fir.extensions.FirExtension
 import org.jetbrains.kotlin.fir.extensions.predicateBasedProvider
 import org.jetbrains.kotlin.fir.moduleData
@@ -27,9 +28,11 @@ import org.jetbrains.kotlin.fir.symbols.impl.FirRegularClassSymbol
 import org.jetbrains.kotlin.fir.types.*
 import org.jetbrains.kotlin.fir.types.builder.buildResolvedTypeRef
 import org.jetbrains.kotlin.name.Name
+import org.jetbrains.kotlin.name.StandardClassIds
 import org.jetbrains.kotlin.platform.isJs
 import org.jetbrains.kotlin.platform.isWasm
 import org.jetbrains.kotlin.platform.konan.isNative
+import org.jetbrains.kotlin.types.ConstantValueKind
 import org.jetbrains.kotlin.utils.addToStdlib.firstIsInstanceOrNull
 import org.jetbrains.kotlinx.serialization.compiler.fir.services.dependencySerializationInfoProvider
 import org.jetbrains.kotlinx.serialization.compiler.resolve.SerialEntityNames
@@ -280,3 +283,32 @@ fun FirDeclaration.excludeFromJsExport() {
 
     replaceAnnotations(annotations + jsExportIgnoreAnnotationCall)
 }
+
+context(FirExtension)
+fun createDeprecatedHiddenAnnotation(): FirAnnotation = buildAnnotation {
+    val deprecatedAnno =
+        session.symbolProvider.getClassLikeSymbolByClassId(StandardClassIds.Annotations.Deprecated) as FirRegularClassSymbol
+
+    annotationTypeRef = deprecatedAnno.defaultType().toFirResolvedTypeRef()
+
+    argumentMapping = buildAnnotationArgumentMapping {
+        mapping[Name.identifier("message")] = buildLiteralExpression(
+            null,
+            ConstantValueKind.String,
+            "This synthesized declaration should not be used directly",
+            setType = true
+        )
+
+        // It has nothing to do with enums deserialization, but it is simply easier to build it this way.
+        mapping[Name.identifier("level")] = buildEnumEntryDeserializedAccessExpression {
+            enumClassId = StandardClassIds.DeprecationLevel
+            enumEntryName = Name.identifier("HIDDEN")
+        }.toQualifiedPropertyAccessExpression(session)
+    }
+}
+
+context(FirExtension)
+fun FirClassLikeDeclaration.markAsDeprecatedHidden() {
+    replaceAnnotations(annotations + listOf(createDeprecatedHiddenAnnotation()))
+    replaceDeprecationsProvider(this.getDeprecationsProvider(session))
+}
diff --git a/plugins/kotlinx-serialization/testData/diagnostics/GeneratedSerializerInaccessible.kt b/plugins/kotlinx-serialization/testData/diagnostics/GeneratedSerializerInaccessible.kt
new file mode 100644
index 00000000000..861a1af2eb0
--- /dev/null
+++ b/plugins/kotlinx-serialization/testData/diagnostics/GeneratedSerializerInaccessible.kt
@@ -0,0 +1,14 @@
+// FIR_IDENTICAL
+// WITH_STDLIB
+// SKIP_TXT
+
+import kotlinx.serialization.*
+
+@Serializable
+class A
+
+fun foo() {
+    A.<!DEPRECATION_ERROR!>`$serializer`<!>
+    A.<!DEPRECATION_ERROR!>`$serializer`<!>.descriptor
+    A(<!TOO_MANY_ARGUMENTS!>0<!>, <!TOO_MANY_ARGUMENTS!>null<!>)
+}
diff --git a/plugins/kotlinx-serialization/testData/firMembers/abstractAndSealed.fir.txt b/plugins/kotlinx-serialization/testData/firMembers/abstractAndSealed.fir.txt
index f4187d35825..5149ef69dd7 100644
--- a/plugins/kotlinx-serialization/testData/firMembers/abstractAndSealed.fir.txt
+++ b/plugins/kotlinx-serialization/testData/firMembers/abstractAndSealed.fir.txt
@@ -70,7 +70,7 @@ FILE: abstractAndSealed.kt
 
         }
 
-        public final object $serializer : R|kotlinx/serialization/internal/GeneratedSerializer<Bottom>| {
+        @R|kotlin/Deprecated|(message = String(This synthesized declaration should not be used directly), level = Q|kotlin/DeprecationLevel|.R|kotlin/DeprecationLevel.HIDDEN|) public final object $serializer : R|kotlinx/serialization/internal/GeneratedSerializer<Bottom>| {
             public final override fun serialize(encoder: R|kotlinx/serialization/encoding/Encoder|, value: R|Bottom|): R|kotlin/Unit|
 
             public final override fun deserialize(decoder: R|kotlinx/serialization/encoding/Decoder|): R|Bottom|
diff --git a/plugins/kotlinx-serialization/testData/firMembers/classWithCompanionObject.fir.txt b/plugins/kotlinx-serialization/testData/firMembers/classWithCompanionObject.fir.txt
index b8db4e3bbef..75c7e3c709a 100644
--- a/plugins/kotlinx-serialization/testData/firMembers/classWithCompanionObject.fir.txt
+++ b/plugins/kotlinx-serialization/testData/firMembers/classWithCompanionObject.fir.txt
@@ -16,7 +16,7 @@ FILE: classWithCompanionObject.kt
 
         }
 
-        public final object $serializer : R|kotlinx/serialization/internal/GeneratedSerializer<SomeClass>| {
+        @R|kotlin/Deprecated|(message = String(This synthesized declaration should not be used directly), level = Q|kotlin/DeprecationLevel|.R|kotlin/DeprecationLevel.HIDDEN|) public final object $serializer : R|kotlinx/serialization/internal/GeneratedSerializer<SomeClass>| {
             public final override fun serialize(encoder: R|kotlinx/serialization/encoding/Encoder|, value: R|SomeClass|): R|kotlin/Unit|
 
             public final override fun deserialize(decoder: R|kotlinx/serialization/encoding/Decoder|): R|SomeClass|
diff --git a/plugins/kotlinx-serialization/testData/firMembers/classWithGenericParameters.fir.txt b/plugins/kotlinx-serialization/testData/firMembers/classWithGenericParameters.fir.txt
index e12ab6d84c8..34387564d23 100644
--- a/plugins/kotlinx-serialization/testData/firMembers/classWithGenericParameters.fir.txt
+++ b/plugins/kotlinx-serialization/testData/firMembers/classWithGenericParameters.fir.txt
@@ -22,7 +22,7 @@ FILE: classWithGenericParameters.kt
 
         }
 
-        public final class $serializer<T, V> : R|kotlinx/serialization/internal/GeneratedSerializer<GenericBox<T, V>>| {
+        @R|kotlin/Deprecated|(message = String(This synthesized declaration should not be used directly), level = Q|kotlin/DeprecationLevel|.R|kotlin/DeprecationLevel.HIDDEN|) public final class $serializer<T, V> : R|kotlinx/serialization/internal/GeneratedSerializer<GenericBox<T, V>>| {
             public final override fun serialize(encoder: R|kotlinx/serialization/encoding/Encoder|, value: R|GenericBox<T, V>|): R|kotlin/Unit|
 
             public final override fun deserialize(decoder: R|kotlinx/serialization/encoding/Decoder|): R|GenericBox<T, V>|
diff --git a/plugins/kotlinx-serialization/testData/firMembers/defaultProperties.fir.txt b/plugins/kotlinx-serialization/testData/firMembers/defaultProperties.fir.txt
index ed3e58e09f2..31a8faf7705 100644
--- a/plugins/kotlinx-serialization/testData/firMembers/defaultProperties.fir.txt
+++ b/plugins/kotlinx-serialization/testData/firMembers/defaultProperties.fir.txt
@@ -33,7 +33,7 @@ FILE: defaultProperties.kt
 
         }
 
-        public final object $serializer : R|kotlinx/serialization/internal/GeneratedSerializer<SomeClass>| {
+        @R|kotlin/Deprecated|(message = String(This synthesized declaration should not be used directly), level = Q|kotlin/DeprecationLevel|.R|kotlin/DeprecationLevel.HIDDEN|) public final object $serializer : R|kotlinx/serialization/internal/GeneratedSerializer<SomeClass>| {
             public final override fun serialize(encoder: R|kotlinx/serialization/encoding/Encoder|, value: R|SomeClass|): R|kotlin/Unit|
 
             public final override fun deserialize(decoder: R|kotlinx/serialization/encoding/Decoder|): R|SomeClass|
diff --git a/plugins/kotlinx-serialization/testData/firMembers/enums.fir.txt b/plugins/kotlinx-serialization/testData/firMembers/enums.fir.txt
index 24af2c7db24..99cdccec3eb 100644
--- a/plugins/kotlinx-serialization/testData/firMembers/enums.fir.txt
+++ b/plugins/kotlinx-serialization/testData/firMembers/enums.fir.txt
@@ -74,7 +74,7 @@ FILE: enums.kt
 
         }
 
-        public final object $serializer : R|kotlinx/serialization/internal/GeneratedSerializer<Holder>| {
+        @R|kotlin/Deprecated|(message = String(This synthesized declaration should not be used directly), level = Q|kotlin/DeprecationLevel|.R|kotlin/DeprecationLevel.HIDDEN|) public final object $serializer : R|kotlinx/serialization/internal/GeneratedSerializer<Holder>| {
             public final override fun serialize(encoder: R|kotlinx/serialization/encoding/Encoder|, value: R|Holder|): R|kotlin/Unit|
 
             public final override fun deserialize(decoder: R|kotlinx/serialization/encoding/Decoder|): R|Holder|
diff --git a/plugins/kotlinx-serialization/testData/firMembers/inlineClasses.fir.txt b/plugins/kotlinx-serialization/testData/firMembers/inlineClasses.fir.txt
index 4775842db2f..5fb76f68744 100644
--- a/plugins/kotlinx-serialization/testData/firMembers/inlineClasses.fir.txt
+++ b/plugins/kotlinx-serialization/testData/firMembers/inlineClasses.fir.txt
@@ -16,7 +16,7 @@ FILE: inlineClasses.kt
 
         }
 
-        public final object $serializer : R|kotlinx/serialization/internal/GeneratedSerializer<Foo>| {
+        @R|kotlin/Deprecated|(message = String(This synthesized declaration should not be used directly), level = Q|kotlin/DeprecationLevel|.R|kotlin/DeprecationLevel.HIDDEN|) public final object $serializer : R|kotlinx/serialization/internal/GeneratedSerializer<Foo>| {
             public final override fun serialize(encoder: R|kotlinx/serialization/encoding/Encoder|, value: R|Foo|): R|kotlin/Unit|
 
             public final override fun deserialize(decoder: R|kotlinx/serialization/encoding/Decoder|): R|Foo|
@@ -50,7 +50,7 @@ FILE: inlineClasses.kt
 
         }
 
-        public final object $serializer : R|kotlinx/serialization/internal/GeneratedSerializer<Holder>| {
+        @R|kotlin/Deprecated|(message = String(This synthesized declaration should not be used directly), level = Q|kotlin/DeprecationLevel|.R|kotlin/DeprecationLevel.HIDDEN|) public final object $serializer : R|kotlinx/serialization/internal/GeneratedSerializer<Holder>| {
             public final override fun serialize(encoder: R|kotlinx/serialization/encoding/Encoder|, value: R|Holder|): R|kotlin/Unit|
 
             public final override fun deserialize(decoder: R|kotlinx/serialization/encoding/Decoder|): R|Holder|
diff --git a/plugins/kotlinx-serialization/testData/firMembers/metaSerializable.fir.txt b/plugins/kotlinx-serialization/testData/firMembers/metaSerializable.fir.txt
index a2b783a7a9a..1a953dd2ff9 100644
--- a/plugins/kotlinx-serialization/testData/firMembers/metaSerializable.fir.txt
+++ b/plugins/kotlinx-serialization/testData/firMembers/metaSerializable.fir.txt
@@ -37,7 +37,7 @@ FILE: metaSerializable.kt
 
         }
 
-        public final object $serializer : R|kotlinx/serialization/internal/GeneratedSerializer<Project1>| {
+        @R|kotlin/Deprecated|(message = String(This synthesized declaration should not be used directly), level = Q|kotlin/DeprecationLevel|.R|kotlin/DeprecationLevel.HIDDEN|) public final object $serializer : R|kotlinx/serialization/internal/GeneratedSerializer<Project1>| {
             public final override fun serialize(encoder: R|kotlinx/serialization/encoding/Encoder|, value: R|Project1|): R|kotlin/Unit|
 
             public final override fun deserialize(decoder: R|kotlinx/serialization/encoding/Decoder|): R|Project1|
@@ -74,7 +74,7 @@ FILE: metaSerializable.kt
 
         }
 
-        public final object $serializer : R|kotlinx/serialization/internal/GeneratedSerializer<Project2>| {
+        @R|kotlin/Deprecated|(message = String(This synthesized declaration should not be used directly), level = Q|kotlin/DeprecationLevel|.R|kotlin/DeprecationLevel.HIDDEN|) public final object $serializer : R|kotlinx/serialization/internal/GeneratedSerializer<Project2>| {
             public final override fun serialize(encoder: R|kotlinx/serialization/encoding/Encoder|, value: R|Project2|): R|kotlin/Unit|
 
             public final override fun deserialize(decoder: R|kotlinx/serialization/encoding/Decoder|): R|Project2|
@@ -108,7 +108,7 @@ FILE: metaSerializable.kt
 
         }
 
-        public final object $serializer : R|kotlinx/serialization/internal/GeneratedSerializer<Wrapper>| {
+        @R|kotlin/Deprecated|(message = String(This synthesized declaration should not be used directly), level = Q|kotlin/DeprecationLevel|.R|kotlin/DeprecationLevel.HIDDEN|) public final object $serializer : R|kotlinx/serialization/internal/GeneratedSerializer<Wrapper>| {
             public final override fun serialize(encoder: R|kotlinx/serialization/encoding/Encoder|, value: R|Wrapper|): R|kotlin/Unit|
 
             public final override fun deserialize(decoder: R|kotlinx/serialization/encoding/Decoder|): R|Wrapper|
@@ -145,7 +145,7 @@ FILE: metaSerializable.kt
 
         }
 
-        public final object $serializer : R|kotlinx/serialization/internal/GeneratedSerializer<Project3>| {
+        @R|kotlin/Deprecated|(message = String(This synthesized declaration should not be used directly), level = Q|kotlin/DeprecationLevel|.R|kotlin/DeprecationLevel.HIDDEN|) public final object $serializer : R|kotlinx/serialization/internal/GeneratedSerializer<Project3>| {
             public final override fun serialize(encoder: R|kotlinx/serialization/encoding/Encoder|, value: R|Project3|): R|kotlin/Unit|
 
             public final override fun deserialize(decoder: R|kotlinx/serialization/encoding/Decoder|): R|Project3|
@@ -205,7 +205,7 @@ FILE: metaSerializable.kt
 
             }
 
-            public final object $serializer : R|kotlinx/serialization/internal/GeneratedSerializer<TestSealed.A>| {
+            @R|kotlin/Deprecated|(message = String(This synthesized declaration should not be used directly), level = Q|kotlin/DeprecationLevel|.R|kotlin/DeprecationLevel.HIDDEN|) public final object $serializer : R|kotlinx/serialization/internal/GeneratedSerializer<TestSealed.A>| {
                 public final override fun serialize(encoder: R|kotlinx/serialization/encoding/Encoder|, value: R|TestSealed.A|): R|kotlin/Unit|
 
                 public final override fun deserialize(decoder: R|kotlinx/serialization/encoding/Decoder|): R|TestSealed.A|
@@ -240,7 +240,7 @@ FILE: metaSerializable.kt
 
             }
 
-            public final object $serializer : R|kotlinx/serialization/internal/GeneratedSerializer<TestSealed.B>| {
+            @R|kotlin/Deprecated|(message = String(This synthesized declaration should not be used directly), level = Q|kotlin/DeprecationLevel|.R|kotlin/DeprecationLevel.HIDDEN|) public final object $serializer : R|kotlinx/serialization/internal/GeneratedSerializer<TestSealed.B>| {
                 public final override fun serialize(encoder: R|kotlinx/serialization/encoding/Encoder|, value: R|TestSealed.B|): R|kotlin/Unit|
 
                 public final override fun deserialize(decoder: R|kotlinx/serialization/encoding/Decoder|): R|TestSealed.B|
@@ -290,7 +290,7 @@ FILE: metaSerializable.kt
 
             }
 
-            public final object $serializer : R|kotlinx/serialization/internal/GeneratedSerializer<TestAbstract.A>| {
+            @R|kotlin/Deprecated|(message = String(This synthesized declaration should not be used directly), level = Q|kotlin/DeprecationLevel|.R|kotlin/DeprecationLevel.HIDDEN|) public final object $serializer : R|kotlinx/serialization/internal/GeneratedSerializer<TestAbstract.A>| {
                 public final override fun serialize(encoder: R|kotlinx/serialization/encoding/Encoder|, value: R|TestAbstract.A|): R|kotlin/Unit|
 
                 public final override fun deserialize(decoder: R|kotlinx/serialization/encoding/Decoder|): R|TestAbstract.A|
@@ -325,7 +325,7 @@ FILE: metaSerializable.kt
 
             }
 
-            public final object $serializer : R|kotlinx/serialization/internal/GeneratedSerializer<TestAbstract.B>| {
+            @R|kotlin/Deprecated|(message = String(This synthesized declaration should not be used directly), level = Q|kotlin/DeprecationLevel|.R|kotlin/DeprecationLevel.HIDDEN|) public final object $serializer : R|kotlinx/serialization/internal/GeneratedSerializer<TestAbstract.B>| {
                 public final override fun serialize(encoder: R|kotlinx/serialization/encoding/Encoder|, value: R|TestAbstract.B|): R|kotlin/Unit|
 
                 public final override fun deserialize(decoder: R|kotlinx/serialization/encoding/Decoder|): R|TestAbstract.B|
diff --git a/plugins/kotlinx-serialization/testData/firMembers/multipleProperties.fir.txt b/plugins/kotlinx-serialization/testData/firMembers/multipleProperties.fir.txt
index e0a6334cd87..2b1cfd9f778 100644
--- a/plugins/kotlinx-serialization/testData/firMembers/multipleProperties.fir.txt
+++ b/plugins/kotlinx-serialization/testData/firMembers/multipleProperties.fir.txt
@@ -25,7 +25,7 @@ FILE: multipleProperties.kt
 
         }
 
-        public final object $serializer : R|kotlinx/serialization/internal/GeneratedSerializer<SomeClass>| {
+        @R|kotlin/Deprecated|(message = String(This synthesized declaration should not be used directly), level = Q|kotlin/DeprecationLevel|.R|kotlin/DeprecationLevel.HIDDEN|) public final object $serializer : R|kotlinx/serialization/internal/GeneratedSerializer<SomeClass>| {
             public final override fun serialize(encoder: R|kotlinx/serialization/encoding/Encoder|, value: R|SomeClass|): R|kotlin/Unit|
 
             public final override fun deserialize(decoder: R|kotlinx/serialization/encoding/Decoder|): R|SomeClass|
diff --git a/plugins/kotlinx-serialization/testData/firMembers/privatePropertiesSerialization.fir.txt b/plugins/kotlinx-serialization/testData/firMembers/privatePropertiesSerialization.fir.txt
index 4f1be0f5a59..e6e6c81772a 100644
--- a/plugins/kotlinx-serialization/testData/firMembers/privatePropertiesSerialization.fir.txt
+++ b/plugins/kotlinx-serialization/testData/firMembers/privatePropertiesSerialization.fir.txt
@@ -36,7 +36,7 @@ FILE: privatePropertiesSerialization.kt
 
         }
 
-        public final object $serializer : R|kotlinx/serialization/internal/GeneratedSerializer<Parent>| {
+        @R|kotlin/Deprecated|(message = String(This synthesized declaration should not be used directly), level = Q|kotlin/DeprecationLevel|.R|kotlin/DeprecationLevel.HIDDEN|) public final object $serializer : R|kotlinx/serialization/internal/GeneratedSerializer<Parent>| {
             public final override fun serialize(encoder: R|kotlinx/serialization/encoding/Encoder|, value: R|Parent|): R|kotlin/Unit|
 
             public final override fun deserialize(decoder: R|kotlinx/serialization/encoding/Decoder|): R|Parent|
@@ -67,7 +67,7 @@ FILE: privatePropertiesSerialization.kt
 
         }
 
-        public final object $serializer : R|kotlinx/serialization/internal/GeneratedSerializer<Derived>| {
+        @R|kotlin/Deprecated|(message = String(This synthesized declaration should not be used directly), level = Q|kotlin/DeprecationLevel|.R|kotlin/DeprecationLevel.HIDDEN|) public final object $serializer : R|kotlinx/serialization/internal/GeneratedSerializer<Derived>| {
             public final override fun serialize(encoder: R|kotlinx/serialization/encoding/Encoder|, value: R|Derived|): R|kotlin/Unit|
 
             public final override fun deserialize(decoder: R|kotlinx/serialization/encoding/Decoder|): R|Derived|
diff --git a/plugins/kotlinx-serialization/testData/firMembers/serializableWithCompanion.fir.txt b/plugins/kotlinx-serialization/testData/firMembers/serializableWithCompanion.fir.txt
index d50e12f6708..9c2cfb0af39 100644
--- a/plugins/kotlinx-serialization/testData/firMembers/serializableWithCompanion.fir.txt
+++ b/plugins/kotlinx-serialization/testData/firMembers/serializableWithCompanion.fir.txt
@@ -43,7 +43,7 @@ FILE: serializableWithCompanion.kt
 
         public final fun copy(i: R|kotlin/Int| = this@R|com/example/WithCompanion|.R|com/example/WithCompanion.i|): R|com/example/WithCompanion|
 
-        public final object $serializer : R|kotlinx/serialization/internal/GeneratedSerializer<com/example/WithCompanion>| {
+        @R|kotlin/Deprecated|(message = String(This synthesized declaration should not be used directly), level = Q|kotlin/DeprecationLevel|.R|kotlin/DeprecationLevel.HIDDEN|) public final object $serializer : R|kotlinx/serialization/internal/GeneratedSerializer<com/example/WithCompanion>| {
             public final override fun serialize(encoder: R|kotlinx/serialization/encoding/Encoder|, value: R|com/example/WithCompanion|): R|kotlin/Unit|
 
             public final override fun deserialize(decoder: R|kotlinx/serialization/encoding/Decoder|): R|com/example/WithCompanion|
@@ -85,7 +85,7 @@ FILE: serializableWithCompanion.kt
 
         public final fun copy(i: R|kotlin/Int| = this@R|com/example/WithNamedCompanion|.R|com/example/WithNamedCompanion.i|): R|com/example/WithNamedCompanion|
 
-        public final object $serializer : R|kotlinx/serialization/internal/GeneratedSerializer<com/example/WithNamedCompanion>| {
+        @R|kotlin/Deprecated|(message = String(This synthesized declaration should not be used directly), level = Q|kotlin/DeprecationLevel|.R|kotlin/DeprecationLevel.HIDDEN|) public final object $serializer : R|kotlinx/serialization/internal/GeneratedSerializer<com/example/WithNamedCompanion>| {
             public final override fun serialize(encoder: R|kotlinx/serialization/encoding/Encoder|, value: R|com/example/WithNamedCompanion|): R|kotlin/Unit|
 
             public final override fun deserialize(decoder: R|kotlinx/serialization/encoding/Decoder|): R|com/example/WithNamedCompanion|
diff --git a/plugins/kotlinx-serialization/testData/firMembers/serializerInLocalClass.fir.txt b/plugins/kotlinx-serialization/testData/firMembers/serializerInLocalClass.fir.txt
index 0a714e48ef2..876157d6961 100644
--- a/plugins/kotlinx-serialization/testData/firMembers/serializerInLocalClass.fir.txt
+++ b/plugins/kotlinx-serialization/testData/firMembers/serializerInLocalClass.fir.txt
@@ -21,7 +21,7 @@ FILE: serializerInLocalClass.kt
 
             }
 
-            public final object $serializer : R|kotlinx/serialization/internal/GeneratedSerializer<<local>/Carrier>| {
+            @R|kotlin/Deprecated|(message = String(This synthesized declaration should not be used directly), level = Q|kotlin/DeprecationLevel|.R|kotlin/DeprecationLevel.HIDDEN|) public final object $serializer : R|kotlinx/serialization/internal/GeneratedSerializer<<local>/Carrier>| {
                 public final override fun serialize(encoder: R|kotlinx/serialization/encoding/Encoder|, value: R|<local>/Carrier|): R|kotlin/Unit|
 
                 public final override fun deserialize(decoder: R|kotlinx/serialization/encoding/Decoder|): R|<local>/Carrier|
diff --git a/plugins/kotlinx-serialization/tests-gen/org/jetbrains/kotlinx/serialization/runners/SerializationFirPsiDiagnosticTestGenerated.java b/plugins/kotlinx-serialization/tests-gen/org/jetbrains/kotlinx/serialization/runners/SerializationFirPsiDiagnosticTestGenerated.java
index c8b47dc9d27..b55333c7fd5 100644
--- a/plugins/kotlinx-serialization/tests-gen/org/jetbrains/kotlinx/serialization/runners/SerializationFirPsiDiagnosticTestGenerated.java
+++ b/plugins/kotlinx-serialization/tests-gen/org/jetbrains/kotlinx/serialization/runners/SerializationFirPsiDiagnosticTestGenerated.java
@@ -68,6 +68,12 @@ public class SerializationFirPsiDiagnosticTestGenerated extends AbstractSerializ
       runTest("plugins/kotlinx-serialization/testData/diagnostics/ExternalSerializers.kt");
     }
 
+    @Test
+    @TestMetadata("GeneratedSerializerInaccessible.kt")
+    public void testGeneratedSerializerInaccessible() {
+      runTest("plugins/kotlinx-serialization/testData/diagnostics/GeneratedSerializerInaccessible.kt");
+    }
+
     @Test
     @TestMetadata("GenericArrays.kt")
     public void testGenericArrays() {
diff --git a/plugins/kotlinx-serialization/tests-gen/org/jetbrains/kotlinx/serialization/runners/SerializationPluginDiagnosticTestGenerated.java b/plugins/kotlinx-serialization/tests-gen/org/jetbrains/kotlinx/serialization/runners/SerializationPluginDiagnosticTestGenerated.java
index 90a647dabba..208a85601ff 100644
--- a/plugins/kotlinx-serialization/tests-gen/org/jetbrains/kotlinx/serialization/runners/SerializationPluginDiagnosticTestGenerated.java
+++ b/plugins/kotlinx-serialization/tests-gen/org/jetbrains/kotlinx/serialization/runners/SerializationPluginDiagnosticTestGenerated.java
@@ -65,6 +65,12 @@ public class SerializationPluginDiagnosticTestGenerated extends AbstractSerializ
     runTest("plugins/kotlinx-serialization/testData/diagnostics/ExternalSerializers.kt");
   }
 
+  @Test
+  @TestMetadata("GeneratedSerializerInaccessible.kt")
+  public void testGeneratedSerializerInaccessible() {
+    runTest("plugins/kotlinx-serialization/testData/diagnostics/GeneratedSerializerInaccessible.kt");
+  }
+
   @Test
   @TestMetadata("GenericArrays.kt")
   public void testGenericArrays() {