diff --git a/src/lib.rs b/src/lib.rs
index d21cbee..196cca6 100644
--- a/src/lib.rs
+++ b/src/lib.rs
@@ -2080,6 +2080,7 @@
 
         let mut ack_eliciting = false;
         let mut in_flight = false;
+        let mut has_data = false;
 
         let mut payload_len = 0;
 
@@ -2284,6 +2285,7 @@
             if push_frame_to_pkt!(frames, frame, payload_len, left) {
                 ack_eliciting = true;
                 in_flight = true;
+                has_data = true;
             }
         }
 
@@ -2329,6 +2331,7 @@
                 if push_frame_to_pkt!(frames, frame, payload_len, left) {
                     ack_eliciting = true;
                     in_flight = true;
+                    has_data = true;
                 }
 
                 // If the stream is still flushable, push it to the back of the
@@ -2350,45 +2353,6 @@
             }
         }
 
-        // Try to retransmit old frames on PTO, if there is space left.
-        if self.recovery.loss_probes[epoch] > 0 &&
-            left > cmp::min(
-                frame::MAX_CRYPTO_OVERHEAD,
-                frame::MAX_STREAM_OVERHEAD,
-            ) &&
-            !is_closing
-        {
-            let unacked_iter = self.recovery.sent[epoch]
-                .iter_mut()
-                // Skip packets that have already been acked or lost and packets
-                // that are not in-flight.
-                .filter(|p| p.in_flight && p.time_acked.is_none() && p.time_lost.is_none());
-
-            'unacked_iter: for unacked in unacked_iter {
-                for frame in &unacked.frames {
-                    // Only retransmit CRYPTO and STREAM frames.
-                    match frame {
-                        frame::Frame::Crypto { .. } |
-                        frame::Frame::Stream { .. } => (),
-
-                        _ => continue,
-                    }
-
-                    // Skip frame if it's too big.
-                    if left < frame.wire_len() {
-                        break 'unacked_iter;
-                    }
-
-                    push_frame_to_pkt!(frames, frame.clone(), payload_len, left);
-
-                    ack_eliciting = true;
-                    in_flight = true;
-
-                    break 'unacked_iter;
-                }
-            }
-        }
-
         // Create PING for PTO probe if no other ack-elicitng frame is sent.
         if self.recovery.loss_probes[epoch] > 0 &&
             !ack_eliciting &&
@@ -2525,6 +2489,7 @@
             delivered_time: now,
             recent_delivered_packet_sent_time: now,
             is_app_limited: false,
+            has_data,
         };
 
         self.recovery.on_packet_sent(
diff --git a/src/recovery/cubic.rs b/src/recovery/cubic.rs
index 11e29c9..4f3888d 100644
--- a/src/recovery/cubic.rs
+++ b/src/recovery/cubic.rs
@@ -319,6 +319,7 @@
             delivered_time: now,
             recent_delivered_packet_sent_time: now,
             is_app_limited: false,
+            has_data: false,
         };
 
         // Send 5k x 4 = 20k, higher than default cwnd(~15k)
@@ -456,6 +457,7 @@
             delivered_time: now,
             recent_delivered_packet_sent_time: now,
             is_app_limited: false,
+            has_data: false,
         };
 
         // 1st round.
diff --git a/src/recovery/delivery_rate.rs b/src/recovery/delivery_rate.rs
index bd54d0e..77fd248 100644
--- a/src/recovery/delivery_rate.rs
+++ b/src/recovery/delivery_rate.rs
@@ -204,6 +204,7 @@
             delivered_time: Instant::now(),
             recent_delivered_packet_sent_time: Instant::now(),
             is_app_limited: false,
+            has_data: false,
         };
 
         recovery
@@ -227,6 +228,7 @@
             delivered_time: Instant::now(),
             recent_delivered_packet_sent_time: Instant::now(),
             is_app_limited: false,
+            has_data: false,
         };
 
         recovery
@@ -259,6 +261,7 @@
             delivered_time: Instant::now(),
             recent_delivered_packet_sent_time: Instant::now(),
             is_app_limited: false,
+            has_data: false,
         };
 
         recvry
@@ -280,6 +283,7 @@
             delivered_time: Instant::now(),
             recent_delivered_packet_sent_time: Instant::now(),
             is_app_limited: false,
+            has_data: false,
         };
 
         recvry.app_limited = true;
diff --git a/src/recovery/mod.rs b/src/recovery/mod.rs
index 6988394..1f9e6ae 100644
--- a/src/recovery/mod.rs
+++ b/src/recovery/mod.rs
@@ -55,6 +55,8 @@
 
 const RTT_WINDOW: Duration = Duration::from_secs(300);
 
+const PTO_PROBES_COUNT: usize = 2;
+
 // Congestion Control
 const INITIAL_WINDOW_PACKETS: usize = 10;
 
@@ -91,7 +93,7 @@
 
     loss_time: [Option<Instant>; packet::EPOCH_COUNT],
 
-    pub sent: [VecDeque<Sent>; packet::EPOCH_COUNT],
+    sent: [VecDeque<Sent>; packet::EPOCH_COUNT],
 
     pub lost: [Vec<frame::Frame>; packet::EPOCH_COUNT],
 
@@ -354,7 +356,27 @@
             handshake_completed,
         );
 
-        self.loss_probes[epoch] = 2;
+        let unacked_iter = self.sent[epoch]
+            .iter_mut()
+            // Skip packets that have already been acked or lost, and packets
+            // that don't contain either CRYPTO or STREAM frames.
+            .filter(|p| p.has_data && p.time_acked.is_none() && p.time_lost.is_none())
+            // Only return as many packets as the number of probe packets that
+            // will be sent.
+            .take(PTO_PROBES_COUNT);
+
+        // Retransmit the frames from the oldest sent packets on PTO. However
+        // the packets are not actually declared lost (so there is no effect to
+        // congestion control), we just reschedule the data they carried.
+        //
+        // This will also trigger sending an ACK and retransmitting frames like
+        // HANDSHAKE_DONE and MAX_DATA / MAX_STREAM_DATA as well, in addition
+        // to CRYPTO and STREAM, if the original packet carried them.
+        for unacked in unacked_iter {
+            self.lost[epoch].extend_from_slice(&unacked.frames);
+        }
+
+        self.loss_probes[epoch] = PTO_PROBES_COUNT;
 
         self.pto_count += 1;
 
@@ -823,6 +845,8 @@
     pub recent_delivered_packet_sent_time: Instant,
 
     pub is_app_limited: bool,
+
+    pub has_data: bool,
 }
 
 impl std::fmt::Debug for Sent {
@@ -831,13 +855,14 @@
         write!(f, "pkt_sent_time={:?} ", self.time_sent.elapsed())?;
         write!(f, "pkt_size={:?} ", self.size)?;
         write!(f, "delivered={:?} ", self.delivered)?;
-        write!(f, "delivered_time ={:?} ", self.delivered_time.elapsed())?;
+        write!(f, "delivered_time={:?} ", self.delivered_time.elapsed())?;
         write!(
             f,
             "recent_delivered_packet_sent_time={:?} ",
             self.recent_delivered_packet_sent_time.elapsed()
         )?;
-        write!(f, "is_app_limited={:?} ", self.is_app_limited)?;
+        write!(f, "is_app_limited={} ", self.is_app_limited)?;
+        write!(f, "has_data={} ", self.has_data)?;
 
         Ok(())
     }
@@ -915,6 +940,7 @@
             delivered_time: now,
             recent_delivered_packet_sent_time: now,
             is_app_limited: false,
+            has_data: false,
         };
 
         r.on_packet_sent(p, packet::EPOCH_APPLICATION, true, now, "");
@@ -934,6 +960,7 @@
             delivered_time: now,
             recent_delivered_packet_sent_time: now,
             is_app_limited: false,
+            has_data: false,
         };
 
         r.on_packet_sent(p, packet::EPOCH_APPLICATION, true, now, "");
@@ -953,6 +980,7 @@
             delivered_time: now,
             recent_delivered_packet_sent_time: now,
             is_app_limited: false,
+            has_data: false,
         };
 
         r.on_packet_sent(p, packet::EPOCH_APPLICATION, true, now, "");
@@ -972,6 +1000,7 @@
             delivered_time: now,
             recent_delivered_packet_sent_time: now,
             is_app_limited: false,
+            has_data: false,
         };
 
         r.on_packet_sent(p, packet::EPOCH_APPLICATION, true, now, "");
@@ -1023,6 +1052,7 @@
             delivered_time: now,
             recent_delivered_packet_sent_time: now,
             is_app_limited: false,
+            has_data: false,
         };
 
         r.on_packet_sent(p, packet::EPOCH_APPLICATION, true, now, "");
@@ -1042,6 +1072,7 @@
             delivered_time: now,
             recent_delivered_packet_sent_time: now,
             is_app_limited: false,
+            has_data: false,
         };
 
         r.on_packet_sent(p, packet::EPOCH_APPLICATION, true, now, "");
@@ -1099,6 +1130,7 @@
             delivered_time: now,
             recent_delivered_packet_sent_time: now,
             is_app_limited: false,
+            has_data: false,
         };
 
         r.on_packet_sent(p, packet::EPOCH_APPLICATION, true, now, "");
@@ -1118,6 +1150,7 @@
             delivered_time: now,
             recent_delivered_packet_sent_time: now,
             is_app_limited: false,
+            has_data: false,
         };
 
         r.on_packet_sent(p, packet::EPOCH_APPLICATION, true, now, "");
@@ -1137,6 +1170,7 @@
             delivered_time: now,
             recent_delivered_packet_sent_time: now,
             is_app_limited: false,
+            has_data: false,
         };
 
         r.on_packet_sent(p, packet::EPOCH_APPLICATION, true, now, "");
@@ -1156,6 +1190,7 @@
             delivered_time: now,
             recent_delivered_packet_sent_time: now,
             is_app_limited: false,
+            has_data: false,
         };
 
         r.on_packet_sent(p, packet::EPOCH_APPLICATION, true, now, "");
@@ -1224,6 +1259,7 @@
             delivered_time: now,
             recent_delivered_packet_sent_time: now,
             is_app_limited: false,
+            has_data: false,
         };
 
         r.on_packet_sent(p, packet::EPOCH_APPLICATION, true, now, "");
@@ -1243,6 +1279,7 @@
             delivered_time: now,
             recent_delivered_packet_sent_time: now,
             is_app_limited: false,
+            has_data: false,
         };
 
         r.on_packet_sent(p, packet::EPOCH_APPLICATION, true, now, "");
@@ -1262,6 +1299,7 @@
             delivered_time: now,
             recent_delivered_packet_sent_time: now,
             is_app_limited: false,
+            has_data: false,
         };
 
         r.on_packet_sent(p, packet::EPOCH_APPLICATION, true, now, "");
@@ -1281,6 +1319,7 @@
             delivered_time: now,
             recent_delivered_packet_sent_time: now,
             is_app_limited: false,
+            has_data: false,
         };
 
         r.on_packet_sent(p, packet::EPOCH_APPLICATION, true, now, "");
diff --git a/src/recovery/reno.rs b/src/recovery/reno.rs
index 9bcfcd7..2a1628e 100644
--- a/src/recovery/reno.rs
+++ b/src/recovery/reno.rs
@@ -171,6 +171,7 @@
             delivered_time: std::time::Instant::now(),
             recent_delivered_packet_sent_time: std::time::Instant::now(),
             is_app_limited: false,
+            has_data: false,
         };
 
         // Send 5k x 4 = 20k, higher than default cwnd(~15k)