diff --git a/src/corelib/serialization/qjsoncbor.cpp b/src/corelib/serialization/qjsoncbor.cpp
index 46d2555554..158f1950d0 100644
--- a/src/corelib/serialization/qjsoncbor.cpp
+++ b/src/corelib/serialization/qjsoncbor.cpp
@@ -869,6 +869,7 @@ QVariantMap QCborMap::toVariantMap() const
 QVariantHash QCborMap::toVariantHash() const
 {
     QVariantHash retval;
+    retval.reserve(size());
     for (qsizetype i = 0; i < 2 * size(); i += 2)
         retval.insert(makeString(d.data(), i), d->valueAt(i + 1).toVariant());
     return retval;