diff --git a/quic/api/QuicTransportBase.cpp b/quic/api/QuicTransportBase.cpp
index 387b05ba4..6bcc00e67 100644
--- a/quic/api/QuicTransportBase.cpp
+++ b/quic/api/QuicTransportBase.cpp
@@ -213,6 +213,8 @@ void QuicTransportBase::closeGracefully() {
   }
 }
 
+// TODO: t64691045 change the closeImpl API to include both the sanitized and
+// unsanited error message, remove exceptionCloseWhat_.
 void QuicTransportBase::closeImpl(
     folly::Optional<std::pair<QuicErrorCode, std::string>> errorCode,
     bool drainConnection,
@@ -279,6 +281,13 @@ void QuicTransportBase::closeImpl(
   } else if (errorCode) {
     cancelCode = *errorCode;
   }
+  // cancelCode is used for communicating error message to local app layer.
+  // errorCode will be used for localConnectionError, and sent in close frames.
+  // It's safe to include the unsanitized error message in cancelCode
+  if (exceptionCloseWhat_) {
+    cancelCode.second = exceptionCloseWhat_.value();
+  }
+
   bool isReset = false;
   bool isAbandon = false;
   LocalErrorCode* localError = cancelCode.first.asLocalErrorCode();
@@ -390,11 +399,8 @@ void QuicTransportBase::closeImpl(
     if (noError) {
       connCallback_->onConnectionEnd();
     } else {
-      std::string closeStr = exceptionCloseWhat_
-          ? std::move(exceptionCloseWhat_.value())
-          : cancelCode.second.str();
       connCallback_->onConnectionError(
-          std::make_pair(cancelCode.first, closeStr));
+          std::make_pair(cancelCode.first, cancelCode.second.str()));
     }
   }
 
diff --git a/quic/api/test/QuicTransportBaseTest.cpp b/quic/api/test/QuicTransportBaseTest.cpp
index c74c3fd75..314f60b81 100644
--- a/quic/api/test/QuicTransportBaseTest.cpp
+++ b/quic/api/test/QuicTransportBaseTest.cpp
@@ -1030,6 +1030,36 @@ TEST_F(QuicTransportImplTest, ConnectionErrorOnWrite) {
       QuicErrorCode(LocalErrorCode::CONNECTION_ABANDONED));
 }
 
+TEST_F(QuicTransportImplTest, ReadErrorUnsanitizedErrorMsg) {
+  transport->setServerConnectionId();
+  transport->transportConn->oneRttWriteCipher = test::createNoOpAead();
+  auto stream = transport->createBidirectionalStream().value();
+  MockReadCallback rcb;
+  transport->setReadCallback(stream, &rcb);
+  EXPECT_CALL(rcb, readError(stream, _))
+      .Times(1)
+      .WillOnce(Invoke(
+          [](StreamId,
+             std::pair<QuicErrorCode, folly::Optional<folly::StringPiece>>
+                 error) {
+            EXPECT_EQ("You need to calm down.", *error.second);
+          }));
+
+  EXPECT_CALL(*socketPtr, write(_, _)).WillOnce(Invoke([](auto&, auto&) {
+    throw std::runtime_error("You need to calm down.");
+    return 0;
+  }));
+  QuicSocket::WriteResult result = transport->writeChain(
+      stream,
+      folly::IOBuf::copyBuffer("You are being too loud."),
+      true,
+      false,
+      nullptr);
+  evb->loopOnce();
+
+  EXPECT_TRUE(transport->isClosed());
+}
+
 TEST_F(QuicTransportImplTest, ConnectionErrorUnhandledException) {
   transport->transportConn->oneRttWriteCipher = test::createNoOpAead();
   auto stream = transport->createBidirectionalStream().value();