2 files changed, 78 insertions, 0 deletions

diff --git a/src/corelib/tools/qmap.h b/src/corelib/tools/qmap.h
index 8c15afd9f8..c030a76666 100644
--- a/src/corelib/tools/qmap.h
+++ b/src/corelib/tools/qmap.h
@@ -913,6 +913,27 @@ Q_OUTOFLINE_TEMPLATE typename QMap<Key, T>::iterator QMap<Key, T>::erase(iterato
 
     Q_ASSERT_X(isValidIterator(const_iterator(it)), "QMap::erase", "The specified iterator argument 'it' is invalid");
 
+    if (d->ref.isShared()) {
+        const_iterator oldBegin = constBegin();
+        const_iterator old = const_iterator(it);
+        int backStepsWithSameKey = 0;
+
+        while (old != oldBegin) {
+            --old;
+            if (qMapLessThanKey(old.key(), it.key()))
+                break;
+            ++backStepsWithSameKey;
+        }
+
+        it = find(old.key()); // ensures detach
+        Q_ASSERT_X(it != iterator(d->end()), "QMap::erase", "Unable to locate same key in erase after detach.");
+
+        while (backStepsWithSameKey > 0) {
+            ++it;
+            --backStepsWithSameKey;
+        }
+    }
+
     Node *n = it.i;
     ++it;
     d->deleteNode(n);
diff --git a/tests/auto/corelib/tools/qmap/tst_qmap.cpp b/tests/auto/corelib/tools/qmap/tst_qmap.cpp
index 0742f19a5e..de9fa41feb 100644
--- a/tests/auto/corelib/tools/qmap/tst_qmap.cpp
+++ b/tests/auto/corelib/tools/qmap/tst_qmap.cpp
@@ -87,6 +87,7 @@ private slots:
     void initializerList();
     void testInsertWithHint();
     void testInsertMultiWithHint();
+    void eraseValidIteratorOnSharedMap();
 };
 
 typedef QMap<QString, QString> StringMap;
@@ -1289,6 +1290,62 @@ void tst_QMap::testInsertMultiWithHint()
     QCOMPARE(map.size(), 14);
 }
 
+void tst_QMap::eraseValidIteratorOnSharedMap()
+{
+    QMap<int, int> a, b;
+    a.insert(10, 10);
+    a.insertMulti(10, 40);
+    a.insertMulti(10, 25);
+    a.insertMulti(10, 30);
+    a.insert(20, 20);
+
+    QMap<int, int>::iterator i = a.begin();
+    while (i.value() != 25)
+        ++i;
+
+    b = a;
+    a.erase(i);
+
+    QCOMPARE(b.size(), 5);
+    QCOMPARE(a.size(), 4);
+
+    for (i = a.begin(); i != a.end(); ++i)
+        QVERIFY(i.value() != 25);
+
+    int itemsWith10 = 0;
+    for (i = b.begin(); i != b.end(); ++i)
+        itemsWith10 += (i.key() == 10);
+
+    QCOMPARE(itemsWith10, 4);
+
+    // Border cases
+    QMap <QString, QString> ms1, ms2, ms3;
+    ms1.insert("foo", "bar");
+    ms1.insertMulti("foo", "quux");
+    ms1.insertMulti("foo", "bar");
+
+    QMap <QString, QString>::iterator si = ms1.begin();
+    ms2 = ms1;
+    ms1.erase(si);
+    si = ms1.begin();
+    QCOMPARE(si.value(), QString("quux"));
+    ++si;
+    QCOMPARE(si.value(), QString("bar"));
+
+    si = ms2.begin();
+    ++si;
+    ++si;
+    ms3 = ms2;
+    ms2.erase(si);
+    si = ms2.begin();
+    QCOMPARE(si.value(), QString("bar"));
+    ++si;
+    QCOMPARE(si.value(), QString("quux"));
+
+    QCOMPARE(ms1.size(), 2);
+    QCOMPARE(ms2.size(), 2);
+    QCOMPARE(ms3.size(), 3);
+}
 
 QTEST_APPLESS_MAIN(tst_QMap)
 #include "tst_qmap.moc"