diff --git a/quic/core/frames/quic_connection_close_frame.cc b/quic/core/frames/quic_connection_close_frame.cc
index a7b3d53..63e0aee 100644
--- a/quic/core/frames/quic_connection_close_frame.cc
+++ b/quic/core/frames/quic_connection_close_frame.cc
@@ -6,6 +6,7 @@
 
 #include <memory>
 
+#include "net/third_party/quiche/src/quic/core/quic_constants.h"
 #include "net/third_party/quiche/src/quic/platform/api/quic_str_cat.h"
 
 namespace quic {
@@ -34,7 +35,9 @@
       application_error_code(ietf_application_error_code),
       extracted_error_code(quic_error_code),
       error_details(std::move(error_details)),
-      transport_close_frame_type(0) {}
+      transport_close_frame_type(0) {
+  DCHECK_LE(ietf_application_error_code, kMaxIetfVarInt);
+}
 
 QuicConnectionCloseFrame::QuicConnectionCloseFrame(
     QuicErrorCode quic_error_code,
@@ -45,7 +48,9 @@
       transport_error_code(transport_error_code),
       extracted_error_code(quic_error_code),
       error_details(std::move(error_details)),
-      transport_close_frame_type(transport_frame_type) {}
+      transport_close_frame_type(transport_frame_type) {
+  DCHECK_LE(transport_error_code, kMaxIetfVarInt);
+}
 
 std::ostream& operator<<(
     std::ostream& os,
diff --git a/quic/core/frames/quic_connection_close_frame.h b/quic/core/frames/quic_connection_close_frame.h
index b4f4fd7..b0cef45 100644
--- a/quic/core/frames/quic_connection_close_frame.h
+++ b/quic/core/frames/quic_connection_close_frame.h
@@ -49,8 +49,7 @@
   // - A 16 bit QuicErrorCode, which is used in Google QUIC.
   union {
     QuicIetfTransportErrorCodes transport_error_code;
-    // TODO(fkastenholz): Change this to uint64_t to reflect -22 of the ID.
-    uint16_t application_error_code;
+    uint64_t application_error_code;
     QuicErrorCode quic_error_code;
   };