diff --git a/src/corelib/tools/qhash.h b/src/corelib/tools/qhash.h
index 09766859a9..040feb080b 100644
--- a/src/corelib/tools/qhash.h
+++ b/src/corelib/tools/qhash.h
@@ -1632,8 +1632,10 @@ public:
         detach();
         auto result = d->findOrInsert(key);
         Q_ASSERT(!result.it.atEnd());
-        if (!result.initialized)
+        if (!result.initialized) {
             Node::createInPlace(result.it.node(), key, T());
+            ++m_size;
+        }
         return result.it.node()->value->value;
     }
 
diff --git a/tests/auto/corelib/tools/qhash/tst_qhash.cpp b/tests/auto/corelib/tools/qhash/tst_qhash.cpp
index 50b1248d91..c906924b2b 100644
--- a/tests/auto/corelib/tools/qhash/tst_qhash.cpp
+++ b/tests/auto/corelib/tools/qhash/tst_qhash.cpp
@@ -42,6 +42,7 @@ private slots:
     void qmultihash_qhash_rvalue_ref_ctor();
     void qmultihash_qhash_rvalue_ref_unite();
     void qmultihashUnite();
+    void qmultihashSize();
 
     void compare();
     void compare2();
@@ -2051,6 +2052,78 @@ void tst_QHash::qmultihashUnite()
     }
 }
 
+void tst_QHash::qmultihashSize()
+{
+    // QMultiHash has an extra m_size member that counts the number of values,
+    // while d->size (shared with QHash) counts the number of distinct keys.
+    {
+        QMultiHash<int, int> hash;
+        QCOMPARE(hash.size(), 0);
+        QVERIFY(hash.isEmpty());
+
+        hash.insert(0, 42);
+        QCOMPARE(hash.size(), 1);
+        QVERIFY(!hash.isEmpty());
+
+        hash.insert(0, 42);
+        QCOMPARE(hash.size(), 2);
+        QVERIFY(!hash.isEmpty());
+
+        hash.emplace(0, 42);
+        QCOMPARE(hash.size(), 3);
+        QVERIFY(!hash.isEmpty());
+
+        QCOMPARE(hash.take(0), 42);
+        QCOMPARE(hash.size(), 2);
+        QVERIFY(!hash.isEmpty());
+
+        QCOMPARE(hash.remove(0), 2);
+        QCOMPARE(hash.size(), 0);
+        QVERIFY(hash.isEmpty());
+    }
+
+    {
+        QMultiHash<int, int> hash;
+        hash.emplace(0, 0);
+        hash.emplace(0, 0);
+        QCOMPARE(hash.size(), 2);
+        QVERIFY(!hash.isEmpty());
+
+        hash.emplace(0, 1);
+        QCOMPARE(hash.size(), 3);
+        QVERIFY(!hash.isEmpty());
+
+        QCOMPARE(hash.remove(0, 0), 2);
+        QCOMPARE(hash.size(), 1);
+        QVERIFY(!hash.isEmpty());
+
+        hash.remove(0);
+        QCOMPARE(hash.size(), 0);
+        QVERIFY(hash.isEmpty());
+    }
+
+    {
+        QMultiHash<int, int> hash;
+
+        hash[0] = 0;
+        QCOMPARE(hash.size(), 1);
+        QVERIFY(!hash.isEmpty());
+
+        hash.replace(0, 1);
+        QCOMPARE(hash.size(), 1);
+        QVERIFY(!hash.isEmpty());
+
+        hash.insert(0, 1);
+        hash.erase(hash.cbegin());
+        QCOMPARE(hash.size(), 1);
+        QVERIFY(!hash.isEmpty());
+
+        hash.erase(hash.cbegin());
+        QCOMPARE(hash.size(), 0);
+        QVERIFY(hash.isEmpty());
+    }
+}
+
 void tst_QHash::keys_values_uniqueKeys()
 {
     QMultiHash<QString, int> hash;