diff --git a/http2/adapter/header_validator.cc b/http2/adapter/header_validator.cc
index 0122018..c68ac35 100644
--- a/http2/adapter/header_validator.cc
+++ b/http2/adapter/header_validator.cc
@@ -73,6 +73,10 @@
                        << "]";
         return HEADER_VALUE_INVALID_CHAR;
       }
+      if (value == "101") {
+        // Switching protocols is not allowed on a HTTP/2 stream.
+        return HEADER_VALUE_INVALID_STATUS;
+      }
       status_ = std::string(value);
     }
     pseudo_headers_.push_back(std::string(key));
diff --git a/http2/adapter/header_validator.h b/http2/adapter/header_validator.h
index 2d7585e..dd8ab59 100644
--- a/http2/adapter/header_validator.h
+++ b/http2/adapter/header_validator.h
@@ -28,6 +28,7 @@
     HEADER_NAME_EMPTY,
     HEADER_NAME_INVALID_CHAR,
     HEADER_VALUE_INVALID_CHAR,
+    HEADER_VALUE_INVALID_STATUS,
   };
   HeaderStatus ValidateSingleHeader(absl::string_view key,
                                     absl::string_view value);
diff --git a/http2/adapter/nghttp2_adapter_test.cc b/http2/adapter/nghttp2_adapter_test.cc
index ef5ec8f..fae5d11 100644
--- a/http2/adapter/nghttp2_adapter_test.cc
+++ b/http2/adapter/nghttp2_adapter_test.cc
@@ -1031,6 +1031,77 @@
   EXPECT_THAT(visitor.data(), EqualsFrames({spdy::SpdyFrameType::SETTINGS}));
 }
 
+TEST(NgHttp2AdapterTest, ClientRejects101Response) {
+  DataSavingVisitor visitor;
+  auto adapter = NgHttp2Adapter::CreateClientAdapter(visitor);
+
+  testing::InSequence s;
+
+  const std::vector<const Header> headers1 =
+      ToHeaders({{":method", "GET"},
+                 {":scheme", "http"},
+                 {":authority", "example.com"},
+                 {":path", "/this/is/request/one"},
+                 {"upgrade", "new-protocol"}});
+
+  const int32_t stream_id1 = adapter->SubmitRequest(headers1, nullptr, nullptr);
+  ASSERT_GT(stream_id1, 0);
+
+  EXPECT_CALL(visitor, OnBeforeFrameSent(HEADERS, stream_id1, _, 0x5));
+  EXPECT_CALL(visitor, OnFrameSent(HEADERS, stream_id1, _, 0x5, 0));
+
+  int result = adapter->Send();
+  EXPECT_EQ(0, result);
+  absl::string_view data = visitor.data();
+  EXPECT_THAT(data, testing::StartsWith(spdy::kHttp2ConnectionHeaderPrefix));
+  data.remove_prefix(strlen(spdy::kHttp2ConnectionHeaderPrefix));
+  EXPECT_THAT(data, EqualsFrames({spdy::SpdyFrameType::HEADERS}));
+  visitor.Clear();
+
+  const std::string stream_frames =
+      TestFrameSequence()
+          .ServerPreface()
+          .Headers(1,
+                   {{":status", "101"},
+                    {"server", "my-fake-server"},
+                    {"date", "Tue, 6 Apr 2021 12:54:01 GMT"}},
+                   /*fin=*/false)
+          .Serialize();
+
+  // Server preface (empty SETTINGS)
+  EXPECT_CALL(visitor, OnFrameHeader(0, 0, SETTINGS, 0));
+  EXPECT_CALL(visitor, OnSettingsStart());
+  EXPECT_CALL(visitor, OnSettingsEnd());
+
+  EXPECT_CALL(visitor, OnFrameHeader(1, _, HEADERS, 4));
+  EXPECT_CALL(visitor, OnBeginHeadersForStream(1));
+  EXPECT_CALL(
+      visitor,
+      OnErrorDebug("Invalid HTTP header field was received: frame type: 1, "
+                   "stream: 1, name: [:status], value: [101]"));
+  EXPECT_CALL(
+      visitor,
+      OnInvalidFrame(1, Http2VisitorInterface::InvalidFrameError::kHttpHeader));
+
+  const int64_t stream_result = adapter->ProcessBytes(stream_frames);
+  EXPECT_EQ(static_cast<int64_t>(stream_frames.size()), stream_result);
+
+  EXPECT_CALL(visitor, OnBeforeFrameSent(SETTINGS, 0, 0, 0x1));
+  EXPECT_CALL(visitor, OnFrameSent(SETTINGS, 0, 0, 0x1, 0));
+  EXPECT_CALL(visitor, OnBeforeFrameSent(RST_STREAM, 1, 4, 0x0));
+  EXPECT_CALL(
+      visitor,
+      OnFrameSent(RST_STREAM, 1, 4, 0x0,
+                  static_cast<uint32_t>(Http2ErrorCode::PROTOCOL_ERROR)));
+  EXPECT_CALL(visitor, OnCloseStream(1, Http2ErrorCode::PROTOCOL_ERROR));
+
+  EXPECT_TRUE(adapter->want_write());
+  result = adapter->Send();
+  EXPECT_EQ(0, result);
+  EXPECT_THAT(visitor.data(), EqualsFrames({spdy::SpdyFrameType::SETTINGS,
+                                            spdy::SpdyFrameType::RST_STREAM}));
+}
+
 TEST(NgHttp2AdapterTest, ClientSubmitRequest) {
   DataSavingVisitor visitor;
   auto adapter = NgHttp2Adapter::CreateClientAdapter(visitor);
diff --git a/http2/adapter/oghttp2_adapter_test.cc b/http2/adapter/oghttp2_adapter_test.cc
index 88ebbed..b8e4c61 100644
--- a/http2/adapter/oghttp2_adapter_test.cc
+++ b/http2/adapter/oghttp2_adapter_test.cc
@@ -1253,6 +1253,77 @@
   EXPECT_THAT(visitor.data(), EqualsFrames({spdy::SpdyFrameType::SETTINGS}));
 }
 
+TEST(OgHttp2AdapterClientTest, ClientRejects101Response) {
+  DataSavingVisitor visitor;
+  OgHttp2Adapter::Options options{.perspective = Perspective::kClient};
+  auto adapter = OgHttp2Adapter::Create(visitor, options);
+
+  testing::InSequence s;
+
+  const std::vector<const Header> headers1 =
+      ToHeaders({{":method", "GET"},
+                 {":scheme", "http"},
+                 {":authority", "example.com"},
+                 {":path", "/this/is/request/one"},
+                 {"upgrade", "new-protocol"}});
+
+  const int32_t stream_id1 = adapter->SubmitRequest(headers1, nullptr, nullptr);
+  ASSERT_GT(stream_id1, 0);
+
+  EXPECT_CALL(visitor, OnBeforeFrameSent(SETTINGS, 0, _, 0x0));
+  EXPECT_CALL(visitor, OnFrameSent(SETTINGS, 0, _, 0x0, 0));
+  EXPECT_CALL(visitor, OnBeforeFrameSent(HEADERS, stream_id1, _, 0x5));
+  EXPECT_CALL(visitor, OnFrameSent(HEADERS, stream_id1, _, 0x5, 0));
+
+  int result = adapter->Send();
+  EXPECT_EQ(0, result);
+  absl::string_view data = visitor.data();
+  EXPECT_THAT(data, testing::StartsWith(spdy::kHttp2ConnectionHeaderPrefix));
+  data.remove_prefix(strlen(spdy::kHttp2ConnectionHeaderPrefix));
+  EXPECT_THAT(data, EqualsFrames({spdy::SpdyFrameType::SETTINGS,
+                                  spdy::SpdyFrameType::HEADERS}));
+  visitor.Clear();
+
+  const std::string stream_frames =
+      TestFrameSequence()
+          .ServerPreface()
+          .Headers(1,
+                   {{":status", "101"},
+                    {"server", "my-fake-server"},
+                    {"date", "Tue, 6 Apr 2021 12:54:01 GMT"}},
+                   /*fin=*/false)
+          .Serialize();
+
+  // Server preface (empty SETTINGS)
+  EXPECT_CALL(visitor, OnFrameHeader(0, 0, SETTINGS, 0));
+  EXPECT_CALL(visitor, OnSettingsStart());
+  EXPECT_CALL(visitor, OnSettingsEnd());
+
+  EXPECT_CALL(visitor, OnFrameHeader(1, _, HEADERS, 4));
+  EXPECT_CALL(visitor, OnBeginHeadersForStream(1));
+  EXPECT_CALL(visitor,
+              OnInvalidFrame(
+                  1, Http2VisitorInterface::InvalidFrameError::kHttpMessaging));
+
+  const int64_t stream_result = adapter->ProcessBytes(stream_frames);
+  EXPECT_EQ(static_cast<int64_t>(stream_frames.size()), stream_result);
+
+  EXPECT_CALL(visitor, OnBeforeFrameSent(SETTINGS, 0, 0, 0x1));
+  EXPECT_CALL(visitor, OnFrameSent(SETTINGS, 0, 0, 0x1, 0));
+  EXPECT_CALL(visitor, OnBeforeFrameSent(RST_STREAM, 1, 4, 0x0));
+  EXPECT_CALL(
+      visitor,
+      OnFrameSent(RST_STREAM, 1, 4, 0x0,
+                  static_cast<uint32_t>(Http2ErrorCode::PROTOCOL_ERROR)));
+  EXPECT_CALL(visitor, OnCloseStream(1, Http2ErrorCode::HTTP2_NO_ERROR));
+
+  EXPECT_TRUE(adapter->want_write());
+  result = adapter->Send();
+  EXPECT_EQ(0, result);
+  EXPECT_THAT(visitor.data(), EqualsFrames({spdy::SpdyFrameType::SETTINGS,
+                                            spdy::SpdyFrameType::RST_STREAM}));
+}
+
 TEST(OgHttp2AdapterClientTest, ClientObeysMaxConcurrentStreams) {
   DataSavingVisitor visitor;
   OgHttp2Adapter::Options options{.perspective = Perspective::kClient};
diff --git a/http2/adapter/oghttp2_session.cc b/http2/adapter/oghttp2_session.cc
index c54d335..09ea8a5 100644
--- a/http2/adapter/oghttp2_session.cc
+++ b/http2/adapter/oghttp2_session.cc
@@ -223,7 +223,11 @@
     return;
   }
   const auto validation_result = validator_.ValidateSingleHeader(key, value);
-  if (validation_result != HeaderValidator::HEADER_OK) {
+  if (validation_result == HeaderValidator::HEADER_VALUE_INVALID_STATUS) {
+    QUICHE_VLOG(2) << "RST_STREAM: invalid status found";
+    result_ = Http2VisitorInterface::HEADER_HTTP_MESSAGING;
+    return;
+  } else if (validation_result != HeaderValidator::HEADER_OK) {
     QUICHE_VLOG(2) << "RST_STREAM: invalid header found";
     // TODO(birenroy): consider updating this to return HEADER_HTTP_MESSAGING.
     result_ = Http2VisitorInterface::HEADER_RST_STREAM;