diff --git a/quiche/http2/adapter/oghttp2_adapter_test.cc b/quiche/http2/adapter/oghttp2_adapter_test.cc
index 673ea23..2ccde27 100644
--- a/quiche/http2/adapter/oghttp2_adapter_test.cc
+++ b/quiche/http2/adapter/oghttp2_adapter_test.cc
@@ -3833,6 +3833,67 @@
   EXPECT_EQ(peer_window, kInitialFlowControlWindowSize);
 }
 
+TEST(OgHttp2AdapterTest, WindowUpdateZeroDelta) {
+  DataSavingVisitor visitor;
+  OgHttp2Adapter::Options options;
+  options.perspective = Perspective::kServer;
+  auto adapter = OgHttp2Adapter::Create(visitor, options);
+
+  const std::string data_chunk(kDefaultFramePayloadSizeLimit, 'a');
+  const std::string request =
+      TestFrameSequence()
+          .ClientPreface()
+          .Headers(1,
+                   {{":method", "GET"},
+                    {":scheme", "https"},
+                    {":authority", "example.com"},
+                    {":path", "/"}},
+                   /*fin=*/false)
+          .WindowUpdate(1, 0)
+          .Data(1, "Subsequent frames on stream 1 are not delivered.")
+          .Serialize();
+  // Client preface (empty SETTINGS)
+  EXPECT_CALL(visitor, OnFrameHeader(0, 0, SETTINGS, 0));
+  EXPECT_CALL(visitor, OnSettingsStart());
+  EXPECT_CALL(visitor, OnSettingsEnd());
+  // Stream 1
+  EXPECT_CALL(visitor, OnFrameHeader(1, _, HEADERS, 4));
+  EXPECT_CALL(visitor, OnBeginHeadersForStream(1));
+  EXPECT_CALL(visitor, OnHeaderForStream).Times(4);
+  EXPECT_CALL(visitor, OnEndHeadersForStream(1));
+
+  EXPECT_CALL(visitor, OnFrameHeader(1, 4, WINDOW_UPDATE, 0));
+
+  adapter->ProcessBytes(request);
+
+  EXPECT_TRUE(adapter->want_write());
+  EXPECT_CALL(visitor, OnBeforeFrameSent(SETTINGS, 0, 6, 0x0));
+  EXPECT_CALL(visitor, OnFrameSent(SETTINGS, 0, 6, 0x0, 0));
+
+  EXPECT_CALL(visitor, OnBeforeFrameSent(SETTINGS, 0, 0, 0x1));
+  EXPECT_CALL(visitor, OnFrameSent(SETTINGS, 0, 0, 0x1, 0));
+
+  EXPECT_CALL(visitor, OnBeforeFrameSent(RST_STREAM, 1, _, 0x0));
+  EXPECT_CALL(visitor,
+              OnFrameSent(RST_STREAM, 1, _, 0x0,
+                          static_cast<int>(Http2ErrorCode::PROTOCOL_ERROR)));
+  EXPECT_CALL(visitor, OnCloseStream(1, _));
+
+  adapter->Send();
+
+  const std::string window_update =
+      TestFrameSequence().WindowUpdate(0, 0).Serialize();
+  EXPECT_CALL(visitor, OnFrameHeader(0, 4, WINDOW_UPDATE, 0));
+  EXPECT_CALL(visitor, OnConnectionError(ConnectionError::kFlowControlError));
+  adapter->ProcessBytes(window_update);
+
+  EXPECT_CALL(visitor, OnBeforeFrameSent(GOAWAY, 0, _, 0x0));
+  EXPECT_CALL(visitor,
+              OnFrameSent(GOAWAY, 0, _, 0x0,
+                          static_cast<int>(Http2ErrorCode::PROTOCOL_ERROR)));
+  adapter->Send();
+}
+
 TEST(OgHttp2AdapterTest, WindowUpdateRaisesFlowControlWindowLimit) {
   DataSavingVisitor visitor;
   OgHttp2Adapter::Options options;
diff --git a/quiche/http2/adapter/oghttp2_session.cc b/quiche/http2/adapter/oghttp2_session.cc
index 75d160a..bcec1cd 100644
--- a/quiche/http2/adapter/oghttp2_session.cc
+++ b/quiche/http2/adapter/oghttp2_session.cc
@@ -1430,8 +1430,20 @@
 void OgHttp2Session::OnWindowUpdate(spdy::SpdyStreamId stream_id,
                                     int delta_window_size) {
   if (stream_id == 0) {
+    if (delta_window_size == 0) {
+      // A PROTOCOL_ERROR, according to RFC 9113 Section 6.9.
+      LatchErrorAndNotify(Http2ErrorCode::PROTOCOL_ERROR,
+                          ConnectionError::kFlowControlError);
+      return;
+    }
     connection_send_window_ += delta_window_size;
   } else {
+    if (delta_window_size == 0) {
+      // A PROTOCOL_ERROR, according to RFC 9113 Section 6.9.
+      EnqueueFrame(std::make_unique<spdy::SpdyRstStreamIR>(
+          stream_id, spdy::ERROR_CODE_PROTOCOL_ERROR));
+      return;
+    }
     auto it = stream_map_.find(stream_id);
     if (it == stream_map_.end()) {
       QUICHE_VLOG(1) << "Stream " << stream_id << " not found!";