diff --git a/chrome/content/zotero/overlay.js b/chrome/content/zotero/overlay.js
index 8de42e036d..91fe971f6d 100644
--- a/chrome/content/zotero/overlay.js
+++ b/chrome/content/zotero/overlay.js
@@ -210,6 +210,10 @@ var ZoteroOverlay = new function()
 			// Make visible
 			ZoteroPane.makeVisible();
 			
+			// Warn about unsafe data directory on first display
+			let dataDir = Zotero.getZoteroDirectory();
+			Zotero.checkForUnsafeDataDirectory(dataDir.path);
+
 			// Make sure tags splitter isn't missing for people upgrading from <2.0b7
 			document.getElementById('zotero-tags-splitter').collapsed = false;
 		} else {
diff --git a/chrome/content/zotero/preferences/preferences_advanced.js b/chrome/content/zotero/preferences/preferences_advanced.js
index e5eee66599..de4ea80f65 100644
--- a/chrome/content/zotero/preferences/preferences_advanced.js
+++ b/chrome/content/zotero/preferences/preferences_advanced.js
@@ -198,59 +198,32 @@ Zotero_Preferences.Advanced = {
 	
 	onDataDirUpdate: function (event) {
 		var radiogroup = document.getElementById('dataDir');
-		var path = document.getElementById('dataDirPath');
 		var useDataDir = Zotero.Prefs.get('useDataDir');
+		var newUseDataDir = radiogroup.selectedIndex == 1;
 		
-		// If triggered from the Choose button, don't show the dialog, since
-		// Zotero.chooseZoteroDirectory() (called below due to the radio button
-		// change) shows its own
-		if (event.originalTarget && event.originalTarget.tagName == 'button') {
-			return true;
+		if (newUseDataDir == useDataDir && !useDataDir) {
+			return;
 		}
-		
-		// If changing from default to custom
-		if (!useDataDir) {
-			event.stopPropagation();
-			var file = Zotero.chooseZoteroDirectory(true, false, function () {
-				Zotero_Preferences.openURL('http://zotero.org/support/zotero_data');
-			});
-			radiogroup.selectedIndex = file ? 1 : 0;
-			return !!file;
-		}
-		
-		var ps = Components.classes["@mozilla.org/embedcomp/prompt-service;1"]
-			.getService(Components.interfaces.nsIPromptService);
-		var buttonFlags = ps.BUTTON_POS_0 * ps.BUTTON_TITLE_IS_STRING
-			+ ps.BUTTON_POS_1 * ps.BUTTON_TITLE_CANCEL
-			+ ps.BUTTON_POS_2 * ps.BUTTON_TITLE_IS_STRING;
-		var app = Zotero.appName;
-		var index = ps.confirmEx(window,
-			Zotero.getString('general.restartRequired'),
-			Zotero.getString('general.restartRequiredForChange', app) + '\n\n'
-				+ Zotero.getString('dataDir.moveFilesToNewLocation', app),
-			buttonFlags,
-			Zotero.getString('general.quitApp', app),
-			null,
-			Zotero.getString('general.moreInformation'),
-			null, {});
-		
-		if (index == 0) {
-			useDataDir = !!radiogroup.selectedIndex;
-			// quit() is asynchronous, but set this here just in case
-			Zotero.Prefs.set('useDataDir', useDataDir);
-			var appStartup = Components.classes["@mozilla.org/toolkit/app-startup;1"]
-					.getService(Components.interfaces.nsIAppStartup);
-			appStartup.quit(Components.interfaces.nsIAppStartup.eAttemptQuit);
-		}
-		else if (index == 2) {
+
+		// This call shows a filepicker if needed,
+		// forces a restart if required
+		// and does nothing if cancel was pressed
+		Zotero.chooseZoteroDirectory(true, !newUseDataDir, function () {
 			Zotero_Preferences.openURL('http://zotero.org/support/zotero_data');
-		}
-		
+		});
+		useDataDir = Zotero.Prefs.get('useDataDir');
 		radiogroup.selectedIndex = useDataDir ? 1 : 0;
+		
 		return useDataDir;
 	},
 	
 	
+	chooseDataDir: function(event) {
+		document.getElementById('dataDir').selectedIndex = 1;
+		//this.onDataDirUpdate(event);
+	},
+	
+	
 	getDataDirPath: function () {
 		var desc = Zotero.Prefs.get('dataDir');
 		if (desc == '') {
diff --git a/chrome/content/zotero/preferences/preferences_advanced.xul b/chrome/content/zotero/preferences/preferences_advanced.xul
index 630aa07f1d..6ffc2eda50 100644
--- a/chrome/content/zotero/preferences/preferences_advanced.xul
+++ b/chrome/content/zotero/preferences/preferences_advanced.xul
@@ -181,10 +181,7 @@
 									onsyncfrompreference="return Zotero_Preferences.Advanced.getDataDirPath();"
 									readonly="true" flex="1"/>
 								<button label="&zotero.preferences.dataDir.choose;"
-									oncommand="var file = Zotero.chooseZoteroDirectory(true);
-										if (!file) {
-											event.stopPropagation();
-										}"/>
+									oncommand="return Zotero_Preferences.Advanced.chooseDataDir(event)"/>
 							</hbox>
 						</radiogroup>
 						
diff --git a/chrome/content/zotero/xpcom/file.js b/chrome/content/zotero/xpcom/file.js
index 82976e9da6..3b7b19b713 100644
--- a/chrome/content/zotero/xpcom/file.js
+++ b/chrome/content/zotero/xpcom/file.js
@@ -1024,4 +1024,9 @@ Zotero.File = new function(){
 		
 		throw e;
 	}
+
+
+	this.isDropboxDirectory = function(path) {
+		return path.toLowerCase().indexOf('dropbox') != -1;
+	}
 }
diff --git a/chrome/content/zotero/xpcom/zotero.js b/chrome/content/zotero/xpcom/zotero.js
index 7cbb0ee925..a6efd8c8f9 100644
--- a/chrome/content/zotero/xpcom/zotero.js
+++ b/chrome/content/zotero/xpcom/zotero.js
@@ -381,7 +381,9 @@ Components.utils.import("resource://gre/modules/osfile.jsm");
 					return false;
 				}
 			}
-			
+			if(Zotero.isStandalone) {
+				Zotero.checkForUnsafeDataDirectory(dataDir.path);
+			}
 			// Register shutdown handler to call Zotero.shutdown()
 			var _shutdownObserver = {observe:function() { Zotero.shutdown().done() }};
 			Services.obs.addObserver(_shutdownObserver, "quit-application", false);
@@ -1066,56 +1068,50 @@ Components.utils.import("resource://gre/modules/osfile.jsm");
 				var fp = Components.classes["@mozilla.org/filepicker;1"]
 							.createInstance(nsIFilePicker);
 				fp.init(win, Zotero.getString('dataDir.selectDir'), nsIFilePicker.modeGetFolder);
+				fp.displayDirectory = Zotero.getZoteroDirectory();
 				fp.appendFilters(nsIFilePicker.filterAll);
 				if (fp.show() == nsIFilePicker.returnOK) {
 					var file = fp.file;
-					
-					if (file.directoryEntries.hasMoreElements()) {
-						var dbfile = file.clone();
+					let dialogText = '';
+					let dialogTitle = '';
+
+					// In dropbox folder
+					if (Zotero.File.isDropboxDirectory(file.path)) {
+						dialogTitle = Zotero.getString('general.warning');
+						dialogText = Zotero.getString('dataDir.unsafeLocation.selected.dropbox') + "\n\n"
+								+ Zotero.getString('dataDir.unsafeLocation.selected.useAnyway');
+					}
+					else if (file.directoryEntries.hasMoreElements()) {
+						let dbfile = file.clone();
 						dbfile.append('zotero.sqlite');
 						
 						// Warn if non-empty and no zotero.sqlite
 						if (!dbfile.exists()) {
-							var buttonFlags = ps.STD_YES_NO_BUTTONS;
-							if (moreInfoCallback) {
-								buttonFlags += ps.BUTTON_POS_2 * ps.BUTTON_TITLE_IS_STRING;
-							}
-							var index = ps.confirmEx(null,
-								Zotero.getString('dataDir.selectedDirNonEmpty.title'),
-								Zotero.getString('dataDir.selectedDirNonEmpty.text'),
-								buttonFlags,
-								null,
-								null,
-								moreInfoCallback ? Zotero.getString('general.help') : null,
-								null, {});
-							
-							// Not OK -- return to file picker
-							if (index == 1) {
-								continue;
-							}
-							else if (index == 2) {
-								setTimeout(function () {
-									moreInfoCallback();
-								}, 1);
-								return false;
-							}
+							dialogTitle = Zotero.getString('dataDir.selectedDirNonEmpty.title');
+							dialogText = Zotero.getString('dataDir.selectedDirNonEmpty.text');
 						}
 					}
+					// Directory empty
 					else {
-						var buttonFlags = ps.STD_YES_NO_BUTTONS;
+						dialogTitle = Zotero.getString('dataDir.selectedDirEmpty.title');
+						dialogText = Zotero.getString('dataDir.selectedDirEmpty.text', Zotero.appName) + '\n\n'
+								+ Zotero.getString('dataDir.selectedDirEmpty.useNewDir');
+					}
+					// Warning dialog to be displayed
+					if(dialogText !== '') {
+						let buttonFlags = ps.STD_YES_NO_BUTTONS;
 						if (moreInfoCallback) {
 							buttonFlags += ps.BUTTON_POS_2 * ps.BUTTON_TITLE_IS_STRING;
 						}
-						var index = ps.confirmEx(null,
-							Zotero.getString('dataDir.selectedDirEmpty.title'),
-							Zotero.getString('dataDir.selectedDirEmpty.text', Zotero.appName) + '\n\n'
-								+ Zotero.getString('dataDir.selectedDirEmpty.useNewDir'),
+						let index = ps.confirmEx(null,
+							dialogTitle,
+							dialogText,
 							buttonFlags,
 							null,
 							null,
 							moreInfoCallback ? Zotero.getString('general.moreInformation') : null,
 							null, {});
-						
+
 						// Not OK -- return to file picker
 						if (index == 1) {
 							continue;
@@ -1127,8 +1123,7 @@ Components.utils.import("resource://gre/modules/osfile.jsm");
 							return false;
 						}
 					}
-					
-					
+
 					// Set new data directory
 					Zotero.Prefs.set('dataDir', file.persistentDescriptor);
 					Zotero.Prefs.set('lastDataDir', file.path);
@@ -1156,12 +1151,41 @@ Components.utils.import("resource://gre/modules/osfile.jsm");
 			forceQuitNow ? null : Zotero.getString('general.restartLater'),
 			null, null, {});
 		
-		if (index == 0) {
+		if (forceQuitNow || index == 0) {
 			Services.startup.quit(Components.interfaces.nsIAppStartup.eAttemptQuit);
 		}
 		
 		return useProfileDir ? true : file;
 	}
+
+
+	this.warnOnUnsafeDataDir = true;
+	this.checkForUnsafeDataDirectory = function (path) {
+		if (this.warnOnUnsafeDataDir && Zotero.File.isDropboxDirectory(path)
+				&& Zotero.Prefs.get('warnOnUnsafeDataDir')) {
+			
+			this.warnOnUnsafeDataDir = false;
+			let check = {value: false};
+			let index = Services.prompt.confirmEx(
+				null,
+				Zotero.getString('general.warning'),
+				Zotero.getString('dataDir.unsafeLocation.existing.dropbox') + "\n\n"
+					+ Zotero.getString('dataDir.unsafeLocation.existing.chooseDifferent'),
+				Services.prompt.STD_YES_NO_BUTTONS,
+				null, null, null,
+				Zotero.getString('general.dontShowWarningAgain'),
+				check
+			);
+
+			// Yes - display dialog.
+			if (index == 0) {
+				Zotero.chooseZoteroDirectory(true);
+			}
+			if (check.value) {
+				Zotero.Prefs.set('warnOnUnsafeDataDir', false);
+			}
+		}
+	}
 	
 	
 	/**
diff --git a/chrome/locale/en-US/zotero/zotero.properties b/chrome/locale/en-US/zotero/zotero.properties
index 5a66e11b9a..e66edeb91d 100644
--- a/chrome/locale/en-US/zotero/zotero.properties
+++ b/chrome/locale/en-US/zotero/zotero.properties
@@ -112,6 +112,10 @@ dataDir.notFound						= The Zotero data directory could not be found.
 dataDir.previousDir					= Previous directory:
 dataDir.useProfileDir				= Use %S profile directory
 dataDir.selectDir					= Select a Zotero data directory
+dataDir.unsafeLocation.selected.dropbox = Choosing a data directory within Dropbox may corrupt your database.
+dataDir.unsafeLocation.selected.useAnyway = Use this directory anyway?
+dataDir.unsafeLocation.existing.dropbox = Your Zotero data directory is within Dropbox, which may lead to data corruption.
+dataDir.unsafeLocation.existing.chooseDifferent = Would you like to choose a different location now?
 dataDir.selectedDirNonEmpty.title		= Directory Not Empty
 dataDir.selectedDirNonEmpty.text		= The directory you selected is not empty and does not appear to be a Zotero data directory.\n\nCreate Zotero files in this directory anyway?
 dataDir.selectedDirEmpty.title			= Directory Empty
diff --git a/defaults/preferences/zotero.js b/defaults/preferences/zotero.js
index b02702317d..c748b99b47 100644
--- a/defaults/preferences/zotero.js
+++ b/defaults/preferences/zotero.js
@@ -11,6 +11,7 @@ pref("extensions.zotero.baseAttachmentPath", '');
 pref("extensions.zotero.useDataDir", false);
 pref("extensions.zotero.dataDir", '');
 pref("extensions.zotero.lastDataDir", '');
+pref("extensions.zotero.warnOnUnsafeDataDir", true);
 pref("extensions.zotero.debug.log",false);
 pref("extensions.zotero.debug.stackTrace", false);
 pref("extensions.zotero.debug.store",false);