diff --git a/tests/benchmarks/corelib/tools/qset/tst_bench_qset.cpp b/tests/benchmarks/corelib/tools/qset/tst_bench_qset.cpp
index 5bbec05aab7..e5ad33d661c 100644
--- a/tests/benchmarks/corelib/tools/qset/tst_bench_qset.cpp
+++ b/tests/benchmarks/corelib/tools/qset/tst_bench_qset.cpp
@@ -125,10 +125,12 @@ void tst_QSet::unite_int_data()
 auto build_sets(int lhsSize, int rhsSize, int overlap)
 {
     QSet<int> lhs;
+    lhs.reserve(lhsSize);
     for (int i = 0; i < lhsSize; ++i)
         lhs.insert(i);
 
     QSet<int> rhs;
+    rhs.reserve(rhsSize);
     for (int i = lhsSize - overlap; i < rhsSize + lhsSize - overlap; ++i)
         rhs.insert(i);