diff --git a/Mac/MainWindow/Sidebar/SidebarOutlineDataSource.swift b/Mac/MainWindow/Sidebar/SidebarOutlineDataSource.swift
index d81048636..935b97458 100644
--- a/Mac/MainWindow/Sidebar/SidebarOutlineDataSource.swift
+++ b/Mac/MainWindow/Sidebar/SidebarOutlineDataSource.swift
@@ -262,10 +262,22 @@ private extension SidebarOutlineDataSource {
 		return accounts
 	}
 
+	func accountHasFolderRepresentingAnyDraggedFolders(_ account: Account, _ draggedFolders: Set<PasteboardFolder>) -> Bool {
+		for draggedFolder in draggedFolders {
+			if account.existingFolder(with: draggedFolder.name) != nil {
+				return true
+			}
+		}
+		return false
+	}
+	
 	func validateLocalFolderDrop(_ outlineView: NSOutlineView, _ draggedFolder: PasteboardFolder, _ parentNode: Node, _ index: Int) -> NSDragOperation {
 		guard let dropAccount = parentNode.representedObject as? Account, dropAccount.accountID != draggedFolder.accountID else {
 			return SidebarOutlineDataSource.dragOperationNone
 		}
+		if accountHasFolderRepresentingAnyDraggedFolders(dropAccount, Set([draggedFolder])) {
+			return SidebarOutlineDataSource.dragOperationNone
+		}
 		let updatedIndex = indexWhereDraggedFolderWouldAppear(parentNode, draggedFolder)
 		if index != updatedIndex {
 			outlineView.setDropItem(parentNode, dropChildIndex: updatedIndex)
@@ -277,6 +289,9 @@ private extension SidebarOutlineDataSource {
 		guard let dropAccount = parentNode.representedObject as? Account else {
 			return SidebarOutlineDataSource.dragOperationNone
 		}
+		if accountHasFolderRepresentingAnyDraggedFolders(dropAccount, draggedFolders) {
+			return SidebarOutlineDataSource.dragOperationNone
+		}
 		for draggedFolder in draggedFolders {
 			if dropAccount.accountID == draggedFolder.accountID {
 				return SidebarOutlineDataSource.dragOperationNone