diff --git a/quiche/quic/core/quic_unacked_packet_map.cc b/quiche/quic/core/quic_unacked_packet_map.cc
index 80401dd01..af65ee103 100644
--- a/quiche/quic/core/quic_unacked_packet_map.cc
+++ b/quiche/quic/core/quic_unacked_packet_map.cc
@@ -503,22 +503,21 @@ bool QuicUnackedPacketMap::NotifyFramesAcked(QuicPacketNumber packet_number,
   }
   bool new_data_acked = false;
   const bool is_retransmission = info->transmission_type != NOT_RETRANSMISSION;
-  const QuicFrames* frames = &info->retransmittable_frames;
   quiche::SimpleBufferAllocator allocator;
-  std::optional<QuicFrames> frames_copy;
-  const bool use_copied_frames =
-      !HasDatagramFrame(info->retransmittable_frames);
-
-  if (use_copied_frames) {
-    frames = &frames_copy.emplace(
-        CopyQuicFrames(&allocator, info->retransmittable_frames));
-  }
+  // SECURITY: OnFrameAcked can synchronously call AddSentPacket → push_back
+  // → Relocate, which frees both the deque slab (invalidating |info|) and
+  // each element's InlinedVector heap buffer (invalidating any iterator into
+  // info->retransmittable_frames). The DATAGRAM-frame copy bypass that was
+  // here is unsafe because the same reentrancy is reachable when a DATAGRAM
+  // frame coexists with a MAX_STREAMS frame in the same packet. Always copy.
+  QuicFrames frames_copy =
+      CopyQuicFrames(&allocator, info->retransmittable_frames);
+  const QuicFrames* frames = &frames_copy;
 
   absl::Cleanup cleanup = [&]() {
-    if (use_copied_frames) {
-      DeleteFrames(&frames_copy.value());
-      info = GetMutableTransmissionInfo(packet_number);
-    }
+    DeleteFrames(&frames_copy);
+    // |info| may have been invalidated by deque relocation; re-fetch.
+    info = GetMutableTransmissionInfo(packet_number);
   };
 
   for (const QuicFrame& frame : *frames) {
@@ -548,22 +547,18 @@ void QuicUnackedPacketMap::MaybeAggregateAckedStreamFrame(
   if (session_notifier_ == nullptr) {
     return;
   }
-  const QuicFrames* frames = &info->retransmittable_frames;
   quiche::SimpleBufferAllocator allocator;
-  std::optional<QuicFrames> frames_copy;
-  const bool use_copied_frames =
-      !HasDatagramFrame(info->retransmittable_frames);
-
-  if (use_copied_frames) {
-    frames = &frames_copy.emplace(
-        CopyQuicFrames(&allocator, info->retransmittable_frames));
-  }
+  // SECURITY: same reentrancy hazard as NotifyFramesAcked. Always copy;
+  // always re-fetch |info|. The DATAGRAM-frame bypass that was here left
+  // both the iterator and the caller's |info| pointing into freed memory
+  // when OnFrameAcked → AddSentPacket → Relocate fires.
+  QuicFrames frames_copy =
+      CopyQuicFrames(&allocator, info->retransmittable_frames);
+  const QuicFrames* frames = &frames_copy;
 
   absl::Cleanup cleanup = [&]() {
-    if (use_copied_frames) {
-      DeleteFrames(&frames_copy.value());
-      info = GetMutableTransmissionInfo(packet_number);
-    }
+    DeleteFrames(&frames_copy);
+    info = GetMutableTransmissionInfo(packet_number);
   };
 
   for (const auto& frame : *frames) {