diff --git a/Telegram/SourceFiles/data/data_shared_media.cpp b/Telegram/SourceFiles/data/data_shared_media.cpp
index fe944be8e..2a17e5310 100644
--- a/Telegram/SourceFiles/data/data_shared_media.cpp
+++ b/Telegram/SourceFiles/data/data_shared_media.cpp
@@ -31,6 +31,7 @@ Copyright (c) 2014-2017 John Preston, https://desktop.telegram.org
 #include "info/info_controller.h"
 #include "window/window_controller.h"
 #include "mainwindow.h"
+#include "core/crash_reports.h"
 
 namespace {
 
@@ -224,7 +225,57 @@ base::optional<int> SharedMediaWithLastSlice::indexOfImpl(Value value) const {
 }
 
 base::optional<int> SharedMediaWithLastSlice::indexOf(Value value) const {
-	auto result = indexOfImpl(value);
+	const auto result = indexOfImpl(value);
+	if (result && (*result < 0 || *result >= size())) {
+		// Should not happen.
+		auto info = QStringList();
+		info.push_back("slice:" + QString::number(_slice.size()));
+		info.push_back(_slice.fullCount()
+			? QString::number(*_slice.fullCount())
+			: QString("-"));
+		info.push_back(_slice.skippedBefore()
+			? QString::number(*_slice.skippedBefore())
+			: QString("-"));
+		info.push_back(_slice.skippedAfter()
+			? QString::number(*_slice.skippedAfter())
+			: QString("-"));
+		info.push_back("ending:" + (_ending
+			? QString::number(_ending->size())
+			: QString("-")));
+		info.push_back((_ending && _ending->fullCount())
+			? QString::number(*_ending->fullCount())
+			: QString("-"));
+		info.push_back((_ending && _ending->skippedBefore())
+			? QString::number(*_ending->skippedBefore())
+			: QString("-"));
+		info.push_back((_ending && _ending->skippedAfter())
+			? QString::number(*_ending->skippedAfter())
+			: QString("-"));
+		if (const auto msgId = base::get_if<FullMsgId>(&value)) {
+			info.push_back("value:" + QString::number(msgId->channel));
+			info.push_back(QString::number(msgId->msg));
+			const auto index = _slice.indexOf(*base::get_if<FullMsgId>(&value));
+			info.push_back("index:" + (index
+				? QString::number(*index)
+				: QString("-")));
+		} else if (const auto photo = base::get_if<not_null<PhotoData*>>(&value)) {
+			info.push_back("value:" + QString::number((*photo)->id));
+		} else {
+			info.push_back("value:bad");
+		}
+		info.push_back("isolated:" + QString(Logs::b(isolatedInSlice())));
+		info.push_back("last:" + (_lastPhotoId
+			? QString::number(*_lastPhotoId)
+			: QString("-")));
+		info.push_back("isolated_last:" + (_isolatedLastPhoto
+			? QString(Logs::b(*_isolatedLastPhoto))
+			: QString("-")));
+		info.push_back("skip:" + (lastPhotoSkip()
+			? QString::number(*lastPhotoSkip())
+			: QString("-")));
+		CrashReports::SetAnnotation("DebugInfo", info.join(','));
+		Unexpected("Result in SharedMediaWithLastSlice::indexOf");
+	}
 	return _reversed
 		? (result | func::negate | func::add(size() - 1))
 		: result;
diff --git a/Telegram/SourceFiles/mediaview.cpp b/Telegram/SourceFiles/mediaview.cpp
index a6a21e31d..969da6369 100644
--- a/Telegram/SourceFiles/mediaview.cpp
+++ b/Telegram/SourceFiles/mediaview.cpp
@@ -3037,18 +3037,12 @@ void MediaView::findCurrent() {
 			? (_index | func::add(*_sharedMediaData->skippedBefore()))
 			: base::none;
 		_fullCount = _sharedMediaData->fullCount();
-		if (_index) {
-			Assert(*_index >= 0 && *_index < _sharedMediaData->size());
-		}
 	} else if (_userPhotosData) {
 		_index = _photo ? _userPhotosData->indexOf(_photo->id) : base::none;
 		_fullIndex = _userPhotosData->skippedBefore()
 			? (_index | func::add(*_userPhotosData->skippedBefore()))
 			: base::none;
 		_fullCount = _userPhotosData->fullCount();
-		if (_index) {
-			Assert(*_index >= 0 && *_index < _userPhotosData->size());
-		}
 	} else {
 		_index = _fullIndex = _fullCount = base::none;
 	}