diff --git a/src/libraries/System.Net.Http/src/System/Net/Http/SocketsHttpHandler/Http2Connection.cs b/src/libraries/System.Net.Http/src/System/Net/Http/SocketsHttpHandler/Http2Connection.cs
index 846ed88bc39e6c..1e93b2f208ac42 100644
--- a/src/libraries/System.Net.Http/src/System/Net/Http/SocketsHttpHandler/Http2Connection.cs
+++ b/src/libraries/System.Net.Http/src/System/Net/Http/SocketsHttpHandler/Http2Connection.cs
@@ -1210,7 +1210,7 @@ private async ValueTask<Http2Stream> SendHeadersAsync(HttpRequestMessage request
                 // Construct and initialize the new Http2Stream instance.  It's stream ID must be set below
                 // before the instance is used and stored into the dictionary.  However, we construct it here
                 // so as to avoid the allocation and initialization expense while holding multiple locks.
-                var http2Stream = new Http2Stream(request, this, _initialWindowSize);
+                var http2Stream = new Http2Stream(request, this);
 
                 // Start the write.  This serializes access to write to the connection, and ensures that HEADERS
                 // and CONTINUATION frames stay together, as they must do. We use the lock as well to ensure new
@@ -1233,8 +1233,13 @@ await PerformWriteAsync(totalSize, (thisRef: this, http2Stream, current, remaini
                                 s.thisRef.ThrowShutdownException();
                             }
 
+                            // Now that we're holding the lock, configure the stream.  The lock must be held while
+                            // assigning the stream ID to ensure only one stream gets an ID, and it must be held
+                            // across setting the initial window size (available credit) and storing the stream into
+                            // collection such that window size updates are able to atomically affect all known streams.
+                            s.http2Stream.Initialize(s.thisRef._nextStream, _initialWindowSize);
+
                             // Client-initiated streams are always odd-numbered, so increase by 2.
-                            s.http2Stream.StreamId = s.thisRef._nextStream;
                             s.thisRef._nextStream += 2;
 
                             // We're about to flush the HEADERS frame, so add the stream to the dictionary now.
diff --git a/src/libraries/System.Net.Http/src/System/Net/Http/SocketsHttpHandler/Http2Stream.cs b/src/libraries/System.Net.Http/src/System/Net/Http/SocketsHttpHandler/Http2Stream.cs
index 1372fa52716798..6fc6b3ea827eb4 100644
--- a/src/libraries/System.Net.Http/src/System/Net/Http/SocketsHttpHandler/Http2Stream.cs
+++ b/src/libraries/System.Net.Http/src/System/Net/Http/SocketsHttpHandler/Http2Stream.cs
@@ -89,7 +89,7 @@ private sealed class Http2Stream : IValueTaskSource, IHttpHeadersHandler, IHttpT
             // See comment on ConnectionWindowThreshold.
             private const int StreamWindowThreshold = StreamWindowSize / 8;
 
-            public Http2Stream(HttpRequestMessage request, Http2Connection connection, int initialWindowSize)
+            public Http2Stream(HttpRequestMessage request, Http2Connection connection)
             {
                 _request = request;
                 _connection = connection;
@@ -102,8 +102,6 @@ public Http2Stream(HttpRequestMessage request, Http2Connection connection, int i
                 _responseBuffer = new ArrayBuffer(InitialStreamBufferSize, usePool: true);
 
                 _pendingWindowUpdate = 0;
-                _availableCredit = initialWindowSize;
-
                 _headerBudgetRemaining = connection._pool.Settings._maxResponseHeadersLength * 1024;
 
                 if (_request.Content == null)
@@ -135,13 +133,18 @@ public Http2Stream(HttpRequestMessage request, Http2Connection connection, int i
                     RequestMessage = _request,
                     Content = new HttpConnectionResponseContent()
                 };
-
-                if (NetEventSource.IsEnabled) Trace($"{request}, {nameof(initialWindowSize)}={initialWindowSize}");
             }
 
             private object SyncObject => this; // this isn't handed out to code that may lock on it
 
-            public int StreamId { get; set; }
+            public void Initialize(int streamId, int initialWindowSize)
+            {
+                StreamId = streamId;
+                _availableCredit = initialWindowSize;
+                if (NetEventSource.IsEnabled) Trace($"{_request}, {nameof(initialWindowSize)}={initialWindowSize}");
+            }
+
+            public int StreamId { get; private set; }
 
             public HttpResponseMessage GetAndClearResponse()
             {