diff --git a/src/libraries/System.Runtime/tests/System/TimeZoneInfoTests.cs b/src/libraries/System.Runtime/tests/System/TimeZoneInfoTests.cs
index dc0650c285df72..f7de159162633c 100644
--- a/src/libraries/System.Runtime/tests/System/TimeZoneInfoTests.cs
+++ b/src/libraries/System.Runtime/tests/System/TimeZoneInfoTests.cs
@@ -2165,7 +2165,7 @@ public static void ToSerializedString_FromSerializedString_RoundTrips(TimeZoneIn
             Assert.Equal(serialized, deserializedTimeZone.ToSerializedString());
         }
 
-        [Theory]
+        [ConditionalTheory(typeof(PlatformDetection), nameof(PlatformDetection.IsBinaryFormatterSupported))]
         [MemberData(nameof(SystemTimeZonesTestData))]
         public static void BinaryFormatter_RoundTrips(TimeZoneInfo timeZone)
         {
diff --git a/src/libraries/System.Runtime/tests/System/UnitySerializationHolderTests.cs b/src/libraries/System.Runtime/tests/System/UnitySerializationHolderTests.cs
index 67b6b11f39359b..ca8cab3a11742b 100644
--- a/src/libraries/System.Runtime/tests/System/UnitySerializationHolderTests.cs
+++ b/src/libraries/System.Runtime/tests/System/UnitySerializationHolderTests.cs
@@ -9,7 +9,7 @@ namespace System.Tests
 {
     public class UnitySerializationHolderTests
     {
-        [Fact]
+        [ConditionalFact(typeof(PlatformDetection), nameof(PlatformDetection.IsBinaryFormatterSupported))]
         public void UnitySerializationHolderWithAssemblySingleton()
         {
             const string UnitySerializationHolderAssemblyBase64String = "AAEAAAD/////AQAAAAAAAAAEAQAAAB9TeXN0ZW0uVW5pdHlTZXJpYWxpemF0aW9uSG9sZGVyAwAAAAREYXRhCVVuaXR5VHlwZQxBc3NlbWJseU5hbWUBAAEIBgIAAABLbXNjb3JsaWIsIFZlcnNpb249NC4wLjAuMCwgQ3VsdHVyZT1uZXV0cmFsLCBQdWJsaWNLZXlUb2tlbj1iNzdhNWM1NjE5MzRlMDg5BgAAAAkCAAAACw==";