diff --git a/src/corelib/tools/qduplicatetracker_p.h b/src/corelib/tools/qduplicatetracker_p.h
index 3e29ede3701..4740047356b 100644
--- a/src/corelib/tools/qduplicatetracker_p.h
+++ b/src/corelib/tools/qduplicatetracker_p.h
@@ -45,7 +45,8 @@ class QDuplicateTracker {
 
     char buffer[bufferSize(Prealloc)];
     std::pmr::monotonic_buffer_resource res{buffer, sizeof buffer};
-    std::pmr::unordered_set<T, QHasher<T>> set{Prealloc, &res};
+    using Set = std::pmr::unordered_set<T, QHasher<T>>;
+    Set set{Prealloc, &res};
 #else
     class Set : public QSet<T> {
         qsizetype setSize = 0;
@@ -120,7 +121,20 @@ public:
 
     void clear()
     {
+#ifdef __cpp_lib_memory_resource
+        // The birth defect of std::unordered_set is that both the nodes as
+        // well as the bucket array are allocated from the same allocator, so
+        // if we want to reclaim memory from the freed nodes, we also need to
+        // reclaim the memory for the bucket array.
+
+        set = Set();    // release all memory in `res` (clear() doesn't, and swap() is UB!)
+        res.release();  // restore to initial state (buffer, sizeof buffer)
+                        // m_b_r can't reuse buffers, anyway
+        // now that `res` is reset to the initial state, also reset `set`:
+        set = Set{Prealloc, &res};
+#else
         set.clear();
+#endif // __cpp_lib_memory_resource
     }
 };
 
diff --git a/tests/auto/corelib/tools/qduplicatetracker/tst_qduplicatetracker.cpp b/tests/auto/corelib/tools/qduplicatetracker/tst_qduplicatetracker.cpp
index f370fcf6814..ef8c36e9c55 100644
--- a/tests/auto/corelib/tools/qduplicatetracker/tst_qduplicatetracker.cpp
+++ b/tests/auto/corelib/tools/qduplicatetracker/tst_qduplicatetracker.cpp
@@ -96,13 +96,15 @@ void tst_QDuplicateTracker::clear()
     QVERIFY(!tracker.hasSeen(1));
     QVERIFY(tracker.hasSeen(1));
 
-    tracker.clear();
-    QVERIFY(!tracker.contains(0));
-    QVERIFY(!tracker.hasSeen(0));
-    QVERIFY(tracker.hasSeen(0));
-    QVERIFY(!tracker.hasSeen(1));
-    QVERIFY(tracker.hasSeen(1));
-    QVERIFY(tracker.contains(1));
+    for (int i = 0; i < 100; ++i) {
+        tracker.clear();
+        QVERIFY(!tracker.contains(0));
+        QVERIFY(!tracker.hasSeen(0));
+        QVERIFY(tracker.hasSeen(0));
+        QVERIFY(!tracker.hasSeen(1));
+        QVERIFY(tracker.hasSeen(1));
+        QVERIFY(tracker.contains(1));
+    }
 }
 
 void tst_QDuplicateTracker::appendTo()