diff --git a/src/quic/cid.cc b/src/quic/cid.cc
index fdc636145210b2..1b5fdd861b7a9a 100644
--- a/src/quic/cid.cc
+++ b/src/quic/cid.cc
@@ -20,14 +20,12 @@ CID::CID() : ptr_(&cid_) {
 CID::CID(const ngtcp2_cid& cid) : CID(cid.data, cid.datalen) {}
 
 CID::CID(const uint8_t* data, size_t len) : CID() {
-  DCHECK_GE(len, kMinLength);
   DCHECK_LE(len, kMaxLength);
   ngtcp2_cid_init(&cid_, data, len);
 }
 
 CID::CID(const ngtcp2_cid* cid) : ptr_(cid) {
   CHECK_NOT_NULL(cid);
-  DCHECK_GE(cid->datalen, kMinLength);
   DCHECK_LE(cid->datalen, kMaxLength);
 }
 
diff --git a/src/quic/session.cc b/src/quic/session.cc
index 30f91163418d16..d939edee18e01a 100644
--- a/src/quic/session.cc
+++ b/src/quic/session.cc
@@ -814,6 +814,14 @@ struct Session::Impl final : public MemoryRetainer {
                                                void* user_data,
                                                void* stream_user_data) {
     NGTCP2_CALLBACK_SCOPE(session)
+    // The callback will be invoked with datalen 0 if a zero-length
+    // stream frame with fin flag set is received. In that case, let's
+    // just ignore it.
+    // Per ngtcp2, the range of bytes that are being acknowledged here
+    // are `[offset, offset + datalen]` but we only really care about
+    // the datalen as our accounting does not track the offset and
+    // acknowledges should never come out of order here.
+    if (datalen == 0) return NGTCP2_SUCCESS;
     return session->application().AcknowledgeStreamData(stream_id, datalen)
                ? NGTCP2_SUCCESS
                : NGTCP2_ERR_CALLBACK_FAILURE;
@@ -1387,6 +1395,7 @@ void Session::Close(Session::CloseMethod method) {
   }
 
   STAT_RECORD_TIMESTAMP(Stats, closing_at);
+  impl_->state_->closing = 1;
 
   // With both the DEFAULT and SILENT options, we will proceed to closing
   // the session immediately. All open streams will be immediately destroyed
@@ -1436,7 +1445,7 @@ void Session::Close(Session::CloseMethod method) {
 void Session::FinishClose() {
   // FinishClose() should be called only after, and as a result of, Close()
   // being called first.
-  DCHECK(impl_);
+  DCHECK(!is_destroyed());
   DCHECK(impl_->state_->closing);
 
   // If impl_->Close() returns true, then the session can be destroyed
diff --git a/src/quic/streams.cc b/src/quic/streams.cc
index f1ce7d2e562703..f7b2ed275f9e15 100644
--- a/src/quic/streams.cc
+++ b/src/quic/streams.cc
@@ -1107,7 +1107,7 @@ void Stream::Acknowledge(size_t datalen) {
   DCHECK_GE(datalen, STAT_GET(Stats, max_offset_ack));
   STAT_SET(Stats, max_offset_ack, datalen);
 
-  // // Consumes the given number of bytes in the buffer.
+  // Consumes the given number of bytes in the buffer.
   outbound_->Acknowledge(datalen);
 }