diff --git a/src/csharp/Grpc.Core.Api/AuthContext.cs b/src/csharp/Grpc.Core.Api/AuthContext.cs
index fbec5001f6d..63a4b02020a 100644
--- a/src/csharp/Grpc.Core.Api/AuthContext.cs
+++ b/src/csharp/Grpc.Core.Api/AuthContext.cs
@@ -31,7 +31,7 @@ namespace Grpc.Core
     /// </summary>
     public class AuthContext
     {
-        string peerIdentityPropertyName;
+        string? peerIdentityPropertyName;
         Dictionary<string, List<AuthProperty>> properties;
 
         /// <summary>
@@ -39,7 +39,7 @@ namespace Grpc.Core
         /// </summary>
         /// <param name="peerIdentityPropertyName">Peer identity property name.</param>
         /// <param name="properties">Multimap of auth properties by name.</param>
-        public AuthContext(string peerIdentityPropertyName, Dictionary<string, List<AuthProperty>> properties)
+        public AuthContext(string? peerIdentityPropertyName, Dictionary<string, List<AuthProperty>> properties)
         {
             this.peerIdentityPropertyName = peerIdentityPropertyName;
             this.properties = GrpcPreconditions.CheckNotNull(properties);
@@ -60,7 +60,7 @@ namespace Grpc.Core
         /// Gets the name of the property that indicates the peer identity. Returns <c>null</c>
         /// if the peer is not authenticated.
         /// </summary>
-        public string PeerIdentityPropertyName
+        public string? PeerIdentityPropertyName
         {
             get
             {
diff --git a/src/csharp/Grpc.Core.Api/CallCredentials.cs b/src/csharp/Grpc.Core.Api/CallCredentials.cs
index 47b84e03bfe..fd6e1510519 100644
--- a/src/csharp/Grpc.Core.Api/CallCredentials.cs
+++ b/src/csharp/Grpc.Core.Api/CallCredentials.cs
@@ -54,7 +54,7 @@ namespace Grpc.Core
         /// Populates call credentials configurator with this instance's configuration.
         /// End users never need to invoke this method as it is part of internal implementation.
         /// </summary>
-        public abstract void InternalPopulateConfiguration(CallCredentialsConfiguratorBase configurator, object state);
+        public abstract void InternalPopulateConfiguration(CallCredentialsConfiguratorBase configurator, object? state);
 
         private class CompositeCallCredentials : CallCredentials
         {
@@ -66,7 +66,7 @@ namespace Grpc.Core
                 this.credentials = new List<CallCredentials>(credentials).AsReadOnly();
             }
 
-            public override void InternalPopulateConfiguration(CallCredentialsConfiguratorBase configurator, object state)
+            public override void InternalPopulateConfiguration(CallCredentialsConfiguratorBase configurator, object? state)
             {
                 configurator.SetCompositeCredentials(state, credentials);
             }
@@ -81,7 +81,7 @@ namespace Grpc.Core
                 this.interceptor = GrpcPreconditions.CheckNotNull(interceptor);
             }
 
-            public override void InternalPopulateConfiguration(CallCredentialsConfiguratorBase configurator, object state)
+            public override void InternalPopulateConfiguration(CallCredentialsConfiguratorBase configurator, object? state)
             {
                 configurator.SetAsyncAuthInterceptorCredentials(state, interceptor);
             }
diff --git a/src/csharp/Grpc.Core.Api/CallCredentialsConfiguratorBase.cs b/src/csharp/Grpc.Core.Api/CallCredentialsConfiguratorBase.cs
index 51f8d729a11..c6525ecc896 100644
--- a/src/csharp/Grpc.Core.Api/CallCredentialsConfiguratorBase.cs
+++ b/src/csharp/Grpc.Core.Api/CallCredentialsConfiguratorBase.cs
@@ -29,11 +29,11 @@ namespace Grpc.Core
         /// <summary>
         /// Consumes configuration for composite call credentials.
         /// </summary>
-        public abstract void SetCompositeCredentials(object state, IReadOnlyList<CallCredentials> credentials);
+        public abstract void SetCompositeCredentials(object? state, IReadOnlyList<CallCredentials> credentials);
 
         /// <summary>
         /// Consumes configuration for call credentials created from <c>AsyncAuthInterceptor</c>
         /// </summary>
-        public abstract void SetAsyncAuthInterceptorCredentials(object state, AsyncAuthInterceptor interceptor);
+        public abstract void SetAsyncAuthInterceptorCredentials(object? state, AsyncAuthInterceptor interceptor);
     }
 }
diff --git a/src/csharp/Grpc.Core.Api/IAsyncStreamWriter.cs b/src/csharp/Grpc.Core.Api/IAsyncStreamWriter.cs
index ccf046851a0..b44eba02d02 100644
--- a/src/csharp/Grpc.Core.Api/IAsyncStreamWriter.cs
+++ b/src/csharp/Grpc.Core.Api/IAsyncStreamWriter.cs
@@ -42,6 +42,6 @@ namespace Grpc.Core
         /// Once set, this property maintains its value across subsequent
         /// writes.
         /// </summary>
-        WriteOptions WriteOptions { get; set; }
+        WriteOptions? WriteOptions { get; set; }
     }
 }
diff --git a/src/csharp/Grpc.Core.Api/ServerCallContext.cs b/src/csharp/Grpc.Core.Api/ServerCallContext.cs
index d560d234ea8..dd61e8b944d 100644
--- a/src/csharp/Grpc.Core.Api/ServerCallContext.cs
+++ b/src/csharp/Grpc.Core.Api/ServerCallContext.cs
@@ -97,7 +97,7 @@ namespace Grpc.Core
         /// For streaming response calls, this property is also exposed as on IServerStreamWriter for convenience.
         /// Both properties are backed by the same underlying value.
         /// </summary>
-        public WriteOptions WriteOptions
+        public WriteOptions? WriteOptions
         {
             get
             {
@@ -143,7 +143,7 @@ namespace Grpc.Core
         /// <summary>Provides implementation of a non-virtual public member.</summary>
         protected abstract Status StatusCore { get; set; }
         /// <summary>Provides implementation of a non-virtual public member.</summary>
-        protected abstract WriteOptions WriteOptionsCore { get; set; }
+        protected abstract WriteOptions? WriteOptionsCore { get; set; }
         /// <summary>Provides implementation of a non-virtual public member.</summary>
         protected abstract AuthContext AuthContextCore { get; }
         /// <summary>Provides implementation of a non-virtual public member.</summary>