diff --git a/core/commonMain/src/kotlinx/serialization/internal/Primitives.kt b/core/commonMain/src/kotlinx/serialization/internal/Primitives.kt
index ab2df630f..5de1fe2fe 100644
--- a/core/commonMain/src/kotlinx/serialization/internal/Primitives.kt
+++ b/core/commonMain/src/kotlinx/serialization/internal/Primitives.kt
@@ -15,7 +15,7 @@ import kotlin.native.concurrent.*
 import kotlin.reflect.*
 import kotlin.time.Duration
 
-@Suppress("OPT_IN_USAGE")
+@OptIn(ExperimentalUnsignedTypes::class)
 @SharedImmutable
 private val BUILTIN_SERIALIZERS = mapOf(
     String::class to String.serializer(),
diff --git a/formats/json-tests/commonTest/src/kotlinx/serialization/features/inline/UnsignedIntegersTest.kt b/formats/json-tests/commonTest/src/kotlinx/serialization/features/inline/UnsignedIntegersTest.kt
index c67fc751b..c01d15409 100644
--- a/formats/json-tests/commonTest/src/kotlinx/serialization/features/inline/UnsignedIntegersTest.kt
+++ b/formats/json-tests/commonTest/src/kotlinx/serialization/features/inline/UnsignedIntegersTest.kt
@@ -95,7 +95,7 @@ class UnsignedIntegersTest : JsonTestBase() {
         assertJsonFormAndRestored(ULong.serializer(), 9223372036854775817U, "9223372036854775817")
     }
 
-    @Suppress("OPT_IN_USAGE")
+    @OptIn(ExperimentalUnsignedTypes::class)
     @Test
     fun testRootArrays() = parametrizedTest {
         assertJsonFormAndRestoredCustom(
@@ -124,7 +124,7 @@ class UnsignedIntegersTest : JsonTestBase() {
     }
 
 //    TODO uncomment when Kotlin 1.8.0 is released
-//    @Suppress("OPT_IN_USAGE")
+//    @OptIn(ExperimentalUnsignedTypes::class)
 //    fun testArrays() {
 //        val data = UnsignedArrays(
 //            ubyteArrayOf(1U, 220U),