diff --git a/Directory.Build.props b/Directory.Build.props
index 59015ed0e..c063a25f0 100644
--- a/Directory.Build.props
+++ b/Directory.Build.props
@@ -19,6 +19,9 @@
     <EmbedUntrackedSources>true</EmbedUntrackedSources>
     <LangVersion>8.0</LangVersion>
     <Nullable>enable</Nullable>
+
+    <!-- Fix CS1900 error in .NET 5 preview -->
+    <AnalysisLevel>4</AnalysisLevel>
   </PropertyGroup>
 
 </Project>
diff --git a/src/Grpc.Net.Client.Web/GrpcWebHandler.cs b/src/Grpc.Net.Client.Web/GrpcWebHandler.cs
index f83450d97..18aa35cef 100644
--- a/src/Grpc.Net.Client.Web/GrpcWebHandler.cs
+++ b/src/Grpc.Net.Client.Web/GrpcWebHandler.cs
@@ -124,7 +124,9 @@ private async Task<HttpResponseMessage> SendAsyncCore(HttpRequestMessage request
             // return content once the entire response has been downloaded. This breaks server streaming.
             //
             // https://github.com/mono/mono/issues/18718
+#pragma warning disable CS0618 // Type or member is obsolete
             request.Properties[WebAssemblyEnableStreamingResponseKey] = true;
+#pragma warning restore CS0618 // Type or member is obsolete
 
             if (HttpVersion != null)
             {
diff --git a/test/Grpc.Net.Client.Tests/Web/GrpcWebHandlerTests.cs b/test/Grpc.Net.Client.Tests/Web/GrpcWebHandlerTests.cs
index 09f70662b..adc8e1eb2 100644
--- a/test/Grpc.Net.Client.Tests/Web/GrpcWebHandlerTests.cs
+++ b/test/Grpc.Net.Client.Tests/Web/GrpcWebHandlerTests.cs
@@ -141,7 +141,9 @@ private class TestHttpHandler : HttpMessageHandler
             protected override Task<HttpResponseMessage> SendAsync(HttpRequestMessage request, CancellationToken cancellationToken)
             {
                 RequestVersion = request.Version;
+#pragma warning disable CS0618 // Type or member is obsolete
                 if (request.Properties.TryGetValue(GrpcWebHandler.WebAssemblyEnableStreamingResponseKey, out var enableStreaming))
+#pragma warning restore CS0618 // Type or member is obsolete
                 {
                     WebAssemblyEnableStreamingResponse = (bool)enableStreaming!;
                 }