diff --git a/http2/adapter/oghttp2_session.cc b/http2/adapter/oghttp2_session.cc
index 21dd589..379a40b 100644
--- a/http2/adapter/oghttp2_session.cc
+++ b/http2/adapter/oghttp2_session.cc
@@ -36,60 +36,50 @@
   void VisitData(const spdy::SpdyDataIR& data) override {
     frame_type_ = static_cast<uint8_t>(data.frame_type());
     stream_id_ = data.stream_id();
-    length_ =
-        data.data_len() + (data.padded() ? 1 : 0) + data.padding_payload_len();
     flags_ = (data.fin() ? 0x1 : 0) | (data.padded() ? 0x8 : 0);
   }
   void VisitHeaders(const spdy::SpdyHeadersIR& headers) override {
     frame_type_ = static_cast<uint8_t>(headers.frame_type());
     stream_id_ = headers.stream_id();
-    length_ = headers.size() - spdy::kFrameHeaderSize;
     flags_ = 0x4 | (headers.fin() ? 0x1 : 0) | (headers.padded() ? 0x8 : 0) |
              (headers.has_priority() ? 0x20 : 0);
   }
   void VisitPriority(const spdy::SpdyPriorityIR& priority) override {
     frame_type_ = static_cast<uint8_t>(priority.frame_type());
     frame_type_ = 2;
-    length_ = 5;
     stream_id_ = priority.stream_id();
   }
   void VisitRstStream(const spdy::SpdyRstStreamIR& rst_stream) override {
     frame_type_ = static_cast<uint8_t>(rst_stream.frame_type());
     frame_type_ = 3;
-    length_ = 4;
     stream_id_ = rst_stream.stream_id();
     error_code_ = rst_stream.error_code();
   }
   void VisitSettings(const spdy::SpdySettingsIR& settings) override {
     frame_type_ = static_cast<uint8_t>(settings.frame_type());
     frame_type_ = 4;
-    length_ = 6 * settings.values().size();
     flags_ = (settings.is_ack() ? 0x1 : 0);
   }
   void VisitPushPromise(const spdy::SpdyPushPromiseIR& push_promise) override {
     frame_type_ = static_cast<uint8_t>(push_promise.frame_type());
     frame_type_ = 5;
-    length_ = push_promise.size() - spdy::kFrameHeaderSize;
     stream_id_ = push_promise.stream_id();
     flags_ = (push_promise.padded() ? 0x8 : 0);
   }
   void VisitPing(const spdy::SpdyPingIR& ping) override {
     frame_type_ = static_cast<uint8_t>(ping.frame_type());
     frame_type_ = 6;
-    length_ = 8;
     flags_ = (ping.is_ack() ? 0x1 : 0);
   }
   void VisitGoAway(const spdy::SpdyGoAwayIR& goaway) override {
     frame_type_ = static_cast<uint8_t>(goaway.frame_type());
     frame_type_ = 7;
-    length_ = goaway.size() - spdy::kFrameHeaderSize;
     error_code_ = goaway.error_code();
   }
   void VisitWindowUpdate(
       const spdy::SpdyWindowUpdateIR& window_update) override {
     frame_type_ = static_cast<uint8_t>(window_update.frame_type());
     frame_type_ = 8;
-    length_ = 4;
     stream_id_ = window_update.stream_id();
   }
   void VisitContinuation(
@@ -97,13 +87,11 @@
     frame_type_ = static_cast<uint8_t>(continuation.frame_type());
     stream_id_ = continuation.stream_id();
     flags_ = continuation.end_headers() ? 0x4 : 0;
-    length_ = continuation.size() - spdy::kFrameHeaderSize;
   }
   void VisitUnknown(const spdy::SpdyUnknownIR& unknown) override {
     frame_type_ = static_cast<uint8_t>(unknown.frame_type());
     stream_id_ = unknown.stream_id();
     flags_ = unknown.flags();
-    length_ = unknown.size() - spdy::kFrameHeaderSize;
   }
   void VisitAltSvc(const spdy::SpdyAltSvcIR& /*altsvc*/) override {}
   void VisitPriorityUpdate(
@@ -111,14 +99,12 @@
   void VisitAcceptCh(const spdy::SpdyAcceptChIR& /*accept_ch*/) override {}
 
   uint32_t stream_id() { return stream_id_; }
-  uint32_t length() { return length_; }
   uint32_t error_code() { return error_code_; }
   uint8_t frame_type() { return frame_type_; }
   uint8_t flags() { return flags_; }
 
  private:
   uint32_t stream_id_ = 0;
-  uint32_t length_ = 0;
   uint32_t error_code_ = 0;
   uint8_t frame_type_ = 0;
   uint8_t flags_ = 0;
@@ -457,10 +443,13 @@
     const auto& frame_ptr = frames_.front();
     FrameAttributeCollector c;
     frame_ptr->Visit(&c);
-    visitor_.OnBeforeFrameSent(c.frame_type(), c.stream_id(), c.length(),
-                               c.flags());
-    frame_ptr->Visit(&send_logger_);
+    // Frames can't accurately report their own length; the actual serialized
+    // length must be used instead.
     spdy::SpdySerializedFrame frame = framer_.SerializeFrame(*frame_ptr);
+    const size_t frame_payload_length = frame.size() - spdy::kFrameHeaderSize;
+    frame_ptr->Visit(&send_logger_);
+    visitor_.OnBeforeFrameSent(c.frame_type(), c.stream_id(),
+                               frame_payload_length, c.flags());
     const int64_t result = visitor_.OnReadyToSend(absl::string_view(frame));
     if (result < 0) {
       LatchErrorAndNotify(Http2ErrorCode::INTERNAL_ERROR,
@@ -470,8 +459,8 @@
       // Write blocked.
       return false;
     } else {
-      visitor_.OnFrameSent(c.frame_type(), c.stream_id(), c.length(), c.flags(),
-                           c.error_code());
+      visitor_.OnFrameSent(c.frame_type(), c.stream_id(), frame_payload_length,
+                           c.flags(), c.error_code());
       if (static_cast<FrameType>(c.frame_type()) == FrameType::RST_STREAM) {
         // If this endpoint is resetting the stream, the stream should be
         // closed. This endpoint is already aware of the outbound RST_STREAM and
@@ -482,7 +471,7 @@
       frames_.pop_front();
       if (static_cast<size_t>(result) < frame.size()) {
         // The frame was partially written, so the rest must be buffered.
-        serialized_prefix_.assign(frame.data() + result, frame.size() - result);
+        serialized_prefix_.append(frame.data() + result, frame.size() - result);
         return false;
       }
     }