diff --git a/chrome/content/zotero/preferences/preferences_advanced.js b/chrome/content/zotero/preferences/preferences_advanced.js
index 71d09c17d..0a246bc95 100644
--- a/chrome/content/zotero/preferences/preferences_advanced.js
+++ b/chrome/content/zotero/preferences/preferences_advanced.js
@@ -298,6 +298,12 @@ Zotero_Preferences.Advanced = {
 		var currentDir = Zotero.DataDirectory.dir;
 		var defaultDataDir = Zotero.DataDirectory.defaultDir;
 		
+		if (Zotero.forceDataDir) {
+			document.getElementById('command-line-data-dir-path').textContent = currentDir;
+			document.getElementById('command-line-data-dir').hidden = false;
+			document.getElementById('data-dir').hidden = true;
+		}
+		
 		// Change "Use profile directory" label to home directory location unless using profile dir
 		if (useDataDir || currentDir == defaultDataDir) {
 			document.getElementById('default-data-dir').setAttribute(
diff --git a/chrome/content/zotero/preferences/preferences_advanced.xul b/chrome/content/zotero/preferences/preferences_advanced.xul
index 3f014e517..e77706daa 100644
--- a/chrome/content/zotero/preferences/preferences_advanced.xul
+++ b/chrome/content/zotero/preferences/preferences_advanced.xul
@@ -184,6 +184,11 @@
 							</hbox>
 						</radiogroup>
 						
+						<vbox id="command-line-data-dir" hidden="true">
+							<description id="command-line-data-dir-path"/>
+							<label value="&zotero.preferences.dataDir.viaCommandLine;"/>
+						</vbox>
+						
 						<hbox>
 							<button label="&zotero.preferences.dataDir.reveal;"
 								oncommand="Zotero.DataDirectory.reveal()"/>
diff --git a/chrome/content/zotero/xpcom/dataDirectory.js b/chrome/content/zotero/xpcom/dataDirectory.js
index a6015d4e7..960cd62d7 100644
--- a/chrome/content/zotero/xpcom/dataDirectory.js
+++ b/chrome/content/zotero/xpcom/dataDirectory.js
@@ -54,7 +54,37 @@ Zotero.DataDirectory = {
 	init: Zotero.Promise.coroutine(function* () {
 		var dataDir;
 		var dbFilename = this.getDatabaseFilename();
-		if (Zotero.Prefs.get('useDataDir')) {
+		// Handle directory specified on command line
+		if (Zotero.forceDataDir) {
+			let dir = Zotero.forceDataDir;
+			// Profile subdirectory
+			if (dir == 'profile') {
+				dataDir = OS.Path.join(Zotero.Profile.dir, this.legacyDirName);
+			}
+			// Absolute path
+			else {
+				// Ignore non-absolute paths
+				if ("winIsAbsolute" in OS.Path) {
+					if (!OS.Path.winIsAbsolute(dir)) {
+						dir = false;
+					}
+				}
+				else if (!dir.startsWith('/')) {
+					dir = false;
+				}
+				if (!dir) {
+					throw `-datadir requires an absolute path or 'profile' ('${Zotero.forceDataDir}' given)`;
+				}
+				
+				// Require parent directory to exist
+				if (!(yield OS.File.exists(OS.Path.dirname(dir)))) {
+					throw `Parent directory of -datadir ${dir} not found`;
+				}
+				
+				dataDir = dir;
+			}
+		}
+		else if (Zotero.Prefs.get('useDataDir')) {
 			let prefVal = Zotero.Prefs.get('dataDir');
 			// Convert old persistent descriptor pref to string path and clear obsolete lastDataDir pref
 			//
@@ -660,6 +690,10 @@ Zotero.DataDirectory = {
 			return false;
 		}
 		
+		if (Zotero.forceDataDir) {
+			return false;
+		}
+		
 		// Legacy default or set to legacy default from other program (Standalone/Z4Fx) to share data
 		if (!Zotero.Prefs.get('useDataDir') || this.isLegacy(currentDir)) {
 			return true;
diff --git a/chrome/content/zotero/xpcom/zotero.js b/chrome/content/zotero/xpcom/zotero.js
index 1f38ea1a8..73876628f 100644
--- a/chrome/content/zotero/xpcom/zotero.js
+++ b/chrome/content/zotero/xpcom/zotero.js
@@ -180,6 +180,8 @@ Services.scriptloader.loadSubScript("resource://zotero/polyfill.js");
 				'skipBundledFiles'
 			];
 			opts.filter(opt => options[opt]).forEach(opt => this[opt] = true);
+			
+			this.forceDataDir = options.forceDataDir;
 		}
 		
 		this.mainThread = Services.tm.mainThread;
@@ -378,16 +380,18 @@ Services.scriptloader.loadSubScript("resource://zotero/polyfill.js");
 		}
 		
 		if (!Zotero.isConnector) {
-			yield Zotero.DataDirectory.checkForLostLegacy();
-			if (this.restarting) {
-				return;
-			}
-			
-			yield Zotero.DataDirectory.checkForMigration(
-				dataDir, Zotero.DataDirectory.defaultDir
-			);
-			if (this.skipLoading) {
-				return;
+			if (!this.forceDataDir) {
+				yield Zotero.DataDirectory.checkForLostLegacy();
+				if (this.restarting) {
+					return;
+				}
+				
+				yield Zotero.DataDirectory.checkForMigration(
+					dataDir, Zotero.DataDirectory.defaultDir
+				);
+				if (this.skipLoading) {
+					return;
+				}
 			}
 			
 			// Make sure data directory isn't in Dropbox, etc.
diff --git a/chrome/locale/en-US/zotero/preferences.dtd b/chrome/locale/en-US/zotero/preferences.dtd
index df2367956..2a5e310e3 100644
--- a/chrome/locale/en-US/zotero/preferences.dtd
+++ b/chrome/locale/en-US/zotero/preferences.dtd
@@ -193,6 +193,7 @@
 <!ENTITY zotero.preferences.dataDir.useProfile			"Use profile directory">
 <!ENTITY zotero.preferences.dataDir.custom				"Custom:">
 <!ENTITY zotero.preferences.dataDir.choose				"Choose…">
+<!ENTITY zotero.preferences.dataDir.viaCommandLine        "(specified via command line)">
 <!ENTITY zotero.preferences.dataDir.reveal				"Show Data Directory">
 <!ENTITY zotero.preferences.dataDir.migrate               "Migrate To New Default Location…">
 
diff --git a/chrome/skin/default/zotero/preferences.css b/chrome/skin/default/zotero/preferences.css
index b95549576..d6065a78e 100644
--- a/chrome/skin/default/zotero/preferences.css
+++ b/chrome/skin/default/zotero/preferences.css
@@ -289,3 +289,17 @@ treechildren::-moz-tree-checkbox(checked){
      in your extension or elsewhere. */
   list-style-image: url("chrome://global/skin/checkbox/cbox-check.gif");
 }
+
+/* Advanced pane */
+#command-line-data-dir description {
+	font-size: 12px;
+	cursor: text;
+	-moz-user-select: text;
+}
+
+#command-line-data-dir label {
+	font-size: 11px;
+	font-style: italic;
+	padding-top: .4em;
+	padding-bottom: .4em;
+}
diff --git a/components/zotero-service.js b/components/zotero-service.js
index c38a6a9ab..8ecef0c4e 100644
--- a/components/zotero-service.js
+++ b/components/zotero-service.js
@@ -503,6 +503,8 @@ ZoteroCommandLineHandler.prototype = {
 			zInitOptions.forceDebugLog = 1;
 		}
 		
+		zInitOptions.forceDataDir = cmdLine.handleFlagWithParam("datadir", false);
+		
 		// handler to open Zotero pane at startup in Zotero for Firefox
 		if (!isStandalone() && cmdLine.handleFlag("ZoteroPaneOpen", false)) {
 			zInitOptions.openPane = true;