diff --git a/Telegram/SourceFiles/dialogs/dialogs_indexed_list.cpp b/Telegram/SourceFiles/dialogs/dialogs_indexed_list.cpp
index 5d6b25748..e7a8ee694 100644
--- a/Telegram/SourceFiles/dialogs/dialogs_indexed_list.cpp
+++ b/Telegram/SourceFiles/dialogs/dialogs_indexed_list.cpp
@@ -91,6 +91,19 @@ void IndexedList::movePinned(Row *row, int deltaSign) {
 	}
 	auto history1 = row->history();
 	auto history2 = (*swapPinnedIndexWith)->history();
+
+	// Debug an assertion violation.
+	if (!history2->isPinnedDialog()) {
+		auto myPinnedCount = 0;
+		for_const (auto row, *this) {
+			if (!row->history()->isPinnedDialog()) {
+				break;
+			}
+			++myPinnedCount;
+		}
+		SignalHandlers::setCrashAnnotation("DebugInfo", QString("row index: %1, deltaSign: %2, pinnedCount: %3, myPinnedCount: %4").arg(row->pos()).arg(deltaSign).arg(App::histories().pinnedCount()).arg(myPinnedCount));
+	}
+
 	t_assert(history1->isPinnedDialog());
 	t_assert(history2->isPinnedDialog());
 	auto index1 = history1->getPinnedIndex();
diff --git a/Telegram/SourceFiles/dialogswidget.cpp b/Telegram/SourceFiles/dialogswidget.cpp
index 144a3ed42..4f7c5b97a 100644
--- a/Telegram/SourceFiles/dialogswidget.cpp
+++ b/Telegram/SourceFiles/dialogswidget.cpp
@@ -721,6 +721,20 @@ bool DialogsInner::updateReorderPinned(QPoint localPosition) {
 	auto rowHeight = st::dialogsRowHeight;
 	if (_dragStart.y() > localPosition.y() && _draggingIndex > 0) {
 		shift = -floorclamp(_dragStart.y() - localPosition.y() + (rowHeight / 2), rowHeight, 0, _draggingIndex);
+
+		// Debug an assertion violation.
+		if (shift < 0) {
+			auto index = 0;
+			for_const (auto row, *shownDialogs()) {
+				if (++index >= _draggingIndex + shift) {
+					t_assert(row->history()->isPinnedDialog());
+					if (index >= _draggingIndex) {
+						break;
+					}
+				}
+			}
+		}
+
 		for (auto from = _draggingIndex, to = _draggingIndex + shift; from > to; --from) {
 			shownDialogs()->movePinned(_dragging, -1);
 			std::swap(_pinnedRows[from], _pinnedRows[from - 1]);
@@ -729,6 +743,20 @@ bool DialogsInner::updateReorderPinned(QPoint localPosition) {
 		}
 	} else if (_dragStart.y() < localPosition.y() && _draggingIndex + 1 < pinnedCount) {
 		shift = floorclamp(localPosition.y() - _dragStart.y() + (rowHeight / 2), rowHeight, 0, pinnedCount - _draggingIndex - 1);
+
+		// Debug an assertion violation.
+		if (shift > 0) {
+			auto index = 0;
+			for_const (auto row, *shownDialogs()) {
+				if (++index >= _draggingIndex) {
+					t_assert(row->history()->isPinnedDialog());
+					if (index >= _draggingIndex + shift) {
+						break;
+					}
+				}
+			}
+		}
+
 		for (auto from = _draggingIndex, to = _draggingIndex + shift; from < to; ++from) {
 			shownDialogs()->movePinned(_dragging, 1);
 			std::swap(_pinnedRows[from], _pinnedRows[from + 1]);