Index: qtbase-opensource-src/src/corelib/itemmodels/qsortfilterproxymodel.cpp
===================================================================
--- qtbase-opensource-src.orig/src/corelib/itemmodels/qsortfilterproxymodel.cpp
+++ qtbase-opensource-src/src/corelib/itemmodels/qsortfilterproxymodel.cpp
@@ -1564,6 +1564,7 @@ void QSortFilterProxyModelPrivate::_q_so
     _q_clearMapping();
     // All internal structures are deleted in clear()
     q->endResetModel();
+    create_mapping(QModelIndex());
     update_source_sort_column();
     if (dynamic_sortfilter && update_source_sort_column())
         sort();
@@ -2141,6 +2142,7 @@ void QSortFilterProxyModel::setSourceMod
     connect(d->model, SIGNAL(modelReset()), this, SLOT(_q_sourceReset()));
 
     endResetModel();
+    d->create_mapping(QModelIndex());
     if (d->update_source_sort_column() && d->dynamic_sortfilter)
         d->sort();
 }
Index: qtbase-opensource-src/tests/auto/corelib/itemmodels/qsortfilterproxymodel_common/tst_qsortfilterproxymodel.cpp
===================================================================
--- qtbase-opensource-src.orig/tests/auto/corelib/itemmodels/qsortfilterproxymodel_common/tst_qsortfilterproxymodel.cpp
+++ qtbase-opensource-src/tests/auto/corelib/itemmodels/qsortfilterproxymodel_common/tst_qsortfilterproxymodel.cpp
@@ -2191,6 +2191,35 @@ void tst_QSortFilterProxyModel::changeSo
     QCOMPARE(spy.at(1).at(2).value<QVector<int> >(), expectedChangedRoles);
 }
 
+void tst_QSortFilterProxyModel::changeSourceDataProxySendDataChanged_qtbug87781()
+{
+    QStandardItemModel baseModel;
+    QSortFilterProxyModel proxyModelBefore;
+    QSortFilterProxyModel proxyModelAfter;
+
+    QSignalSpy baseDataChangedSpy(&baseModel, &QStandardItemModel::dataChanged);
+    QSignalSpy beforeDataChangedSpy(&proxyModelBefore, &QSortFilterProxyModel::dataChanged);
+    QSignalSpy afterDataChangedSpy(&proxyModelAfter, &QSortFilterProxyModel::dataChanged);
+
+    QVERIFY(baseDataChangedSpy.isValid());
+    QVERIFY(beforeDataChangedSpy.isValid());
+    QVERIFY(afterDataChangedSpy.isValid());
+
+    proxyModelBefore.setSourceModel(&baseModel);
+    baseModel.insertRows(0, 1);
+    baseModel.insertColumns(0, 1);
+    proxyModelAfter.setSourceModel(&baseModel);
+
+    QCOMPARE(baseDataChangedSpy.size(), 0);
+    QCOMPARE(beforeDataChangedSpy.size(), 0);
+    QCOMPARE(afterDataChangedSpy.size(), 0);
+
+    baseModel.setData(baseModel.index(0, 0), QStringLiteral("new data"), Qt::DisplayRole);
+    QCOMPARE(baseDataChangedSpy.size(), 1);
+    QCOMPARE(beforeDataChangedSpy.size(), 1);
+    QCOMPARE(afterDataChangedSpy.size(), 1);
+}
+
 void tst_QSortFilterProxyModel::sortFilterRole()
 {
     QStandardItemModel model;
Index: qtbase-opensource-src/tests/auto/corelib/itemmodels/qsortfilterproxymodel_common/tst_qsortfilterproxymodel.h
===================================================================
--- qtbase-opensource-src.orig/tests/auto/corelib/itemmodels/qsortfilterproxymodel_common/tst_qsortfilterproxymodel.h
+++ qtbase-opensource-src/tests/auto/corelib/itemmodels/qsortfilterproxymodel_common/tst_qsortfilterproxymodel.h
@@ -90,6 +90,7 @@ private slots:
     void changeSourceData();
     void changeSourceDataKeepsStableSorting_qtbug1548();
     void changeSourceDataForwardsRoles_qtbug35440();
+    void changeSourceDataProxySendDataChanged_qtbug87781();
     void resortingDoesNotBreakTreeModels();
     void dynamicFilterWithoutSort();
     void sortFilterRole();