diff --git a/net/dcsctp/tx/outstanding_data.cc b/net/dcsctp/tx/outstanding_data.cc
index 4972fc5f10..ca639abc54 100644
--- a/net/dcsctp/tx/outstanding_data.cc
+++ b/net/dcsctp/tx/outstanding_data.cc
@@ -240,9 +240,8 @@ void OutstandingData::NackBetweenAckBlocks(
     for (UnwrappedTSN tsn = prev_block_last_acked.next_value();
          tsn < cur_block_first_acked && tsn <= max_tsn_to_nack;
          tsn = tsn.next_value()) {
-      Item& item = GetItem(tsn);
       ack_info.has_packet_loss |=
-          NackItem(tsn, item, /*retransmit_now=*/false,
+          NackItem(tsn, /*retransmit_now=*/false,
                    /*do_fast_retransmit=*/!is_in_fast_recovery);
     }
     prev_block_last_acked = UnwrappedTSN::AddTo(cumulative_tsn_ack, block.end);
@@ -255,9 +254,9 @@ void OutstandingData::NackBetweenAckBlocks(
 }
 
 bool OutstandingData::NackItem(UnwrappedTSN tsn,
-                               Item& item,
                                bool retransmit_now,
                                bool do_fast_retransmit) {
+  Item& item = GetItem(tsn);
   if (item.is_outstanding()) {
     unacked_bytes_ -= GetSerializedChunkSize(item.data());
     --unacked_items_;
@@ -446,13 +445,20 @@ absl::optional<UnwrappedTSN> OutstandingData::Insert(
 
 void OutstandingData::NackAll() {
   UnwrappedTSN tsn = last_cumulative_tsn_ack_;
+  // A two-pass algorithm is needed, as NackItem will invalidate iterators.
+  std::vector<UnwrappedTSN> tsns_to_nack;
   for (Item& item : outstanding_data_) {
     tsn.Increment();
     if (!item.is_acked()) {
-      NackItem(tsn, item, /*retransmit_now=*/true,
-               /*do_fast_retransmit=*/false);
+      tsns_to_nack.push_back(tsn);
     }
   }
+
+  for (UnwrappedTSN tsn : tsns_to_nack) {
+    NackItem(tsn, /*retransmit_now=*/true,
+             /*do_fast_retransmit=*/false);
+  }
+
   RTC_DCHECK(IsConsistent());
 }
 
diff --git a/net/dcsctp/tx/outstanding_data.h b/net/dcsctp/tx/outstanding_data.h
index 82e78337b8..2a214975e6 100644
--- a/net/dcsctp/tx/outstanding_data.h
+++ b/net/dcsctp/tx/outstanding_data.h
@@ -330,10 +330,11 @@ class OutstandingData {
   // many times so that it should be retransmitted, this will schedule it to be
   // "fast retransmitted". This is only done just before going into fast
   // recovery.
-  bool NackItem(UnwrappedTSN tsn,
-                Item& item,
-                bool retransmit_now,
-                bool do_fast_retransmit);
+  //
+  // Note that since nacking an item may result in it becoming abandoned, which
+  // in turn could alter `outstanding_data_`, any iterators are invalidated
+  // after having called this method.
+  bool NackItem(UnwrappedTSN tsn, bool retransmit_now, bool do_fast_retransmit);
 
   // Given that a message fragment, `item` has been abandoned, abandon all other
   // fragments that share the same message - both never-before-sent fragments