diff --git a/src/libraries/System.Text.Json/tests/System.Text.Json.Tests/Utf8JsonWriterTests.cs b/src/libraries/System.Text.Json/tests/System.Text.Json.Tests/Utf8JsonWriterTests.cs
index 45986cccb9aaa5..4515e69412d3f3 100644
--- a/src/libraries/System.Text.Json/tests/System.Text.Json.Tests/Utf8JsonWriterTests.cs
+++ b/src/libraries/System.Text.Json/tests/System.Text.Json.Tests/Utf8JsonWriterTests.cs
@@ -3069,10 +3069,9 @@ public void WritingHugeBase64Bytes(JsonWriterOptions options)
         }
 
         // https://github.com/dotnet/runtime/issues/30746
-        [Theory]
+        [Theory, OuterLoop("Very long running test")]
         [MemberData(nameof(JsonOptions_TestData))]
         [SkipOnCoreClr("https://github.com/dotnet/runtime/issues/45464", ~RuntimeConfiguration.Release)]
-        [OuterLoop("Too slow", typeof(PlatformDetection), nameof(PlatformDetection.IsBrowser))]
         public void Writing3MBBase64Bytes(JsonWriterOptions options)
         {
             byte[] value = new byte[3 * 1024 * 1024];
@@ -4422,7 +4421,7 @@ public void EscapeAsciiCharacters(JsonWriterOptions options)
 
         [Theory]
         [MemberData(nameof(JsonOptions_TestData))]
-        [OuterLoop("Too slow", typeof(PlatformDetection), nameof(PlatformDetection.IsBrowser))]
+        [OuterLoop("Too slow", typeof(PlatformDetection), nameof(PlatformDetection.IsMonoRuntime))]
         public void EscapeCharacters(JsonWriterOptions options)
         {
             // Do not include surrogate pairs.
@@ -5305,7 +5304,7 @@ public void WriteDoubleValue(JsonWriterOptions options, double value)
         [Theory]
         [SkipOnTargetFramework(TargetFrameworkMonikers.NetFramework)]
         [MemberData(nameof(WriteValue_TestData))]
-        [OuterLoop("Too slow", typeof(PlatformDetection), nameof(PlatformDetection.IsBrowser))]
+        [OuterLoop("Too slow", typeof(PlatformDetection), nameof(PlatformDetection.IsMonoRuntime))]
         public void WriteNumbers(JsonWriterOptions options, string keyString)
         {
             var random = new Random(42);