     }
 
     private lazy var compareToolbarButton = UIBarButtonItem(title: CommonStrings.compareTitle, style: .plain, target: self, action: #selector(showDiff(_:)))
-    private lazy var firstComparisonSelectionButton = makeComparisonSelectionButton()
-    private lazy var secondComparisonSelectionButton = makeComparisonSelectionButton()
+    private lazy var firstComparisonSelectionButton: AlignedImageButton = {
+        let button = makeComparisonSelectionButton()
+        button.tag = 0
+        return button
+    }()
+    private lazy var secondComparisonSelectionButton: AlignedImageButton = {
+        let button = makeComparisonSelectionButton()
+        button.tag = 1
+        return button
+    }()
     private var comparisonSelectionButtonWidthConstraints = [NSLayoutConstraint]()
 
     private func makeComparisonSelectionButton() -> AlignedImageButton {

        button.contentHorizontalAlignment = .leading
        button.leftPadding = 10
        button.rightPadding = 10
        return button
    }



    var openSelectionIndex = 0
    private var postedMaxRevisionsSelectedAccessibilityNotification = false
    private var indexPathsSelectedForComparison = [Int: IndexPath]()

    func collectionView(_ collectionView: UICollectionView, didSelectItemAt indexPath: IndexPath) {
        selectedCellsCount += 1
        defer {
