# UNDF: UNDF-2026-000001152
# UNDF:
--- a/tree/tree/src/TTreeCache.cxx
+++ b/tree/tree/src/TTreeCache.cxx
@@ -299,6 +299,7 @@
 #include "TRegexp.h"
 #include "TLeaf.h"
 #include "TFriendElement.h"
 #include "TFile.h"
 #include "TMath.h"
 #include "TBranchCacheInfo.h"
 #include "TVirtualPerfStats.h"
 #include <climits>
+#include <unordered_set>

 #include <memory>
@@ -1378,7 +1378,7 @@
          Int_t nReachedEnd = 0;
          Int_t nSkipped = 0;
          auto oldnReadPrefRequest = nReadPrefRequest;
-         std::vector<Int_t> potentialVetoes;
+         std::unordered_set<Int_t> potentialVetoes;

          if (showMore || gDebug > 7)
             Info("CollectBaskets", "Called with pass=%d narrow=%d maxCollectEntry=%lld", pass, narrow, maxCollectEntry);
@@ -1395,7 +1395,7 @@
             potentialVetoes.clear();
             if (pass == kStart && !cursor[i].fLoadedOnce && resetBranchInfo) {
                // First check if we have any cluster that is currently in the
                // cache but was not used and would be reloaded in the next
                // cluster.
-               b->fCacheInfo.GetUnused(potentialVetoes);
+               { std::vector<Int_t> tmp; b->fCacheInfo.GetUnused(tmp); for (auto v : tmp) potentialVetoes.insert(v); }
                if (showMore || gDebug > 7) {
                   TString vetolist;
                   for(auto v : potentialVetoes) {
@@ -1508,7 +1508,7 @@

-               if (std::find(std::begin(potentialVetoes), std::end(potentialVetoes), j) != std::end(potentialVetoes)) {
+               if (potentialVetoes.count(j)) {
                   // This basket was in the previous cache/cluster and was not used,
                   // let's not read it again. I.e. we bet that it will continue to not
                   // be used.  At worst it will be used and thus read by itself.