diff --git a/src/corelib/tools/qduplicatetracker_p.h b/src/corelib/tools/qduplicatetracker_p.h
index 7e47ab0272a..434285e4907 100644
--- a/src/corelib/tools/qduplicatetracker_p.h
+++ b/src/corelib/tools/qduplicatetracker_p.h
@@ -94,6 +94,11 @@ public:
     {
         return !set.insert(std::move(s)).second;
     }
+    // For when you want to know, but aren't *yet* sure you'll add it:
+    [[nodiscard]] bool contains(const T &s) const
+    {
+        return set.find(s) != set.end(); // TODO C++20: can use set.contains()
+    }
 
     template <typename C>
     void appendTo(C &c) const &
diff --git a/tests/auto/corelib/tools/qduplicatetracker/tst_qduplicatetracker.cpp b/tests/auto/corelib/tools/qduplicatetracker/tst_qduplicatetracker.cpp
index ad0b6abbc70..f370fcf6814 100644
--- a/tests/auto/corelib/tools/qduplicatetracker/tst_qduplicatetracker.cpp
+++ b/tests/auto/corelib/tools/qduplicatetracker/tst_qduplicatetracker.cpp
@@ -24,12 +24,17 @@ void tst_QDuplicateTracker::hasSeen()
 {
     {
         QDuplicateTracker<int, 2> tracker;
+        QVERIFY(!tracker.contains(0));
+        QVERIFY(!tracker.contains(0));
         QVERIFY(!tracker.hasSeen(0));
         QVERIFY(tracker.hasSeen(0));
+        QVERIFY(tracker.contains(0));
         QVERIFY(!tracker.hasSeen(1));
         QVERIFY(tracker.hasSeen(1));
         // past the prealloc amount
+        QVERIFY(!tracker.contains(2));
         QVERIFY(!tracker.hasSeen(2));
+        QVERIFY(tracker.contains(2));
         QVERIFY(tracker.hasSeen(2));
     }
 
@@ -41,12 +46,16 @@ void tst_QDuplicateTracker::hasSeen()
         QString string3("string3");
 
         // Move when seen
+        QVERIFY(!tracker.contains(string1));
         QVERIFY(!tracker.hasSeen(string1));
+        QVERIFY(tracker.contains(string1));
         QVERIFY(tracker.hasSeen(std::move(string1)));
 
         // Move when unseen
+        QVERIFY(!tracker.contains(string2));
         QVERIFY(!tracker.hasSeen(std::move(string2)));
         QVERIFY(tracker.hasSeen(string2_2));
+        QVERIFY(tracker.contains(string2_2));
 
         // Past the prealloc amount
         QVERIFY(!tracker.hasSeen(string3));
@@ -62,17 +71,19 @@ void tst_QDuplicateTracker::hasSeen()
 
         // Move when seen
         QVERIFY(!tracker.hasSeen(string1));
+        QVERIFY(tracker.contains(string1));
         QVERIFY(tracker.hasSeen(std::move(string1)));
 
         // Move when unseen
         QVERIFY(!tracker.hasSeen(std::move(string2)));
         QVERIFY(tracker.hasSeen(string2_2));
+        QVERIFY(tracker.contains(string2_2));
 
         // Past the prealloc amount
+        QVERIFY(!tracker.contains(string3));
         QVERIFY(!tracker.hasSeen(string3));
         QVERIFY(tracker.hasSeen(string3));
     }
-
 }
 
 void tst_QDuplicateTracker::clear()
@@ -80,14 +91,18 @@ void tst_QDuplicateTracker::clear()
     QDuplicateTracker<int, 2> tracker;
     QVERIFY(!tracker.hasSeen(0));
     QVERIFY(tracker.hasSeen(0));
+    QVERIFY(tracker.contains(0));
+    QVERIFY(!tracker.contains(1));
     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));
 }
 
 void tst_QDuplicateTracker::appendTo()