diff --git a/chrome/content/zotero/preferences/preferences_advanced.js b/chrome/content/zotero/preferences/preferences_advanced.js
index b9c1402ae..88ac3fb7b 100644
--- a/chrome/content/zotero/preferences/preferences_advanced.js
+++ b/chrome/content/zotero/preferences/preferences_advanced.js
@@ -48,6 +48,50 @@ Zotero_Preferences.Advanced = {
 		Components.utils.import("resource://zotero/config.js")
 		var ps = Components.classes["@mozilla.org/embedcomp/prompt-service;1"]
 			.getService(Components.interfaces.nsIPromptService);
+		
+		// ~/Zotero exists and is non-empty
+		if ((yield OS.File.exists(defaultDir)) && !(yield Zotero.File.directoryIsEmpty(defaultDir))) {
+			let buttonFlags = (ps.BUTTON_POS_0) * (ps.BUTTON_TITLE_IS_STRING)
+				+ (ps.BUTTON_POS_1) * (ps.BUTTON_TITLE_CANCEL);
+			let index = ps.confirmEx(
+				window,
+				Zotero.getString('general.error'),
+				Zotero.getString('zotero.preferences.advanced.migrateDataDir.directoryExists1', defaultDir)
+					+ "\n\n"
+					+ Zotero.getString('zotero.preferences.advanced.migrateDataDir.directoryExists2'),
+				buttonFlags,
+				Zotero.getString('general.showDirectory'),
+				null, null, null, {}
+			);
+			if (index == 0) {
+				yield Zotero.File.reveal(
+					// Windows opens the directory, which might be confusing here, so open parent instead
+					Zotero.isWin ? OS.Path.dirname(defaultDir) : defaultDir
+				);
+			}
+			return;
+		}
+		
+		var additionalText = '';
+		if (Zotero.isWin) {
+			try {
+				let numItems = yield Zotero.DB.valueQueryAsync(
+					"SELECT COUNT(*) FROM itemAttachments WHERE linkMode IN (?, ?)",
+					[Zotero.Attachments.LINK_MODE_IMPORTED_FILE, Zotero.Attachments.LINK_MODE_IMPORTED_URL]
+				);
+				if (numItems > 100) {
+					additionalText = '\n\n' + Zotero.getString(
+						'zotero.preferences.advanced.migrateDataDir.manualMigration',
+						[Zotero.appName, defaultDir, ZOTERO_CONFIG.CLIENT_NAME]
+					);
+				}
+			}
+			catch (e) {
+				Zotero.logError(e);
+			}
+		}
+		
+		// Prompt to restart
 		var buttonFlags = (ps.BUTTON_POS_0) * (ps.BUTTON_TITLE_IS_STRING)
 					+ (ps.BUTTON_POS_1) * (ps.BUTTON_TITLE_CANCEL);
 		var index = ps.confirmEx(window,
@@ -58,9 +102,9 @@ Zotero_Preferences.Advanced = {
 			) + '\n\n'
 			+ Zotero.getString(
 				'zotero.preferences.advanced.migrateDataDir.appMustBeRestarted', Zotero.appName
-			),
+			) + additionalText,
 			buttonFlags,
-			Zotero.getString('general.restartApp', Zotero.appName),
+			Zotero.getString('general.continue'),
 			null, null, null, {}
 		);
 		
diff --git a/chrome/content/zotero/xpcom/dataDirectory.js b/chrome/content/zotero/xpcom/dataDirectory.js
index 106d3cd15..cd1c89ade 100644
--- a/chrome/content/zotero/xpcom/dataDirectory.js
+++ b/chrome/content/zotero/xpcom/dataDirectory.js
@@ -730,47 +730,13 @@ Zotero.DataDirectory = {
 		
 		// Create the new directory
 		if (!partial) {
-			try {
-				yield OS.File.makeDir(
-					newDir,
-					{
-						ignoreExisting: false,
-						unixMode: 0o755
-					}
-				);
-			}
-			catch (e) {
-				// If default dir exists and is non-empty, move it out of the way
-				// ("Zotero-1", "Zotero-2", …)
-				if (e instanceof OS.File.Error && e.becauseExists) {
-					if (!(yield Zotero.File.directoryIsEmpty(newDir))) {
-						let i = 1;
-						while (true) {
-							let backupDir = newDir + "-" + i++;
-							if (yield OS.File.exists(backupDir)) {
-								if (i > 5) {
-									throw new Error("Too many backup directories "
-										+ "-- stopped at " + backupDir);
-								}
-								continue;
-							}
-							Zotero.debug(`Moving existing directory to ${backupDir}`);
-							yield Zotero.File.moveDirectory(newDir, backupDir);
-							break;
-						}
-						yield OS.File.makeDir(
-							newDir,
-							{
-								ignoreExisting: false,
-								unixMode: 0o755
-							}
-						);
-					}
+			yield OS.File.makeDir(
+				newDir,
+				{
+					ignoreExisting: false,
+					unixMode: 0o755
 				}
-				else {
-					throw e;
-				}
-			}
+			);
 		}
 		
 		// Copy marker
diff --git a/chrome/locale/en-US/zotero/zotero.properties b/chrome/locale/en-US/zotero/zotero.properties
index 9de9d9d28..1bca23f0e 100644
--- a/chrome/locale/en-US/zotero/zotero.properties
+++ b/chrome/locale/en-US/zotero/zotero.properties
@@ -59,6 +59,8 @@ general.dontShowAgain = Don’t Show Again
 general.fix                      = Fix…
 general.tryAgain                 = Try Again
 general.tryLater                 = Try Later
+general.showDirectory = Show Directory
+general.continue = Continue
 
 general.operationInProgress = A Zotero operation is currently in progress.
 general.operationInProgress.waitUntilFinished = Please wait until it has finished.
@@ -639,8 +641,11 @@ zotero.preferences.advanced.resetTranslators.changesLost				= Any new or modifie
 zotero.preferences.advanced.resetStyles								= Reset Styles
 zotero.preferences.advanced.resetStyles.changesLost					= Any new or modified styles will be lost.
 zotero.preferences.advanced.migrateDataDir.title                       = Migrate Data Directory
+zotero.preferences.advanced.migrateDataDir.directoryExists1 = A directory already exists at %S.
+zotero.preferences.advanced.migrateDataDir.directoryExists2 = Please move or rename it and try again.
 zotero.preferences.advanced.migrateDataDir.directoryWillBeMoved        = Your %1$S data directory will be moved to %2$S.
 zotero.preferences.advanced.migrateDataDir.appMustBeRestarted          = %S must be restarted to complete the migration.
+zotero.preferences.advanced.migrateDataDir.manualMigration = You can also quit %1$S and move your existing data directory to %2$S manually, which may be faster for larger data directories. %3$S will automatically detect the new location.
 
 zotero.preferences.advanced.debug.title = Debug Output Submitted
 zotero.preferences.advanced.debug.sent = Debug output has been sent to the Zotero server.\n\nThe Debug ID is D%S.