diff --git a/chrome/content/zotero/merge.js b/chrome/content/zotero/merge.js
index f421f2ddf7..c3c68a9fd2 100644
--- a/chrome/content/zotero/merge.js
+++ b/chrome/content/zotero/merge.js
@@ -46,8 +46,9 @@ var Zotero_Merge_Window = new function () {
 				break;
 			
 			default:
-				throw ("Unsupported merge object type '" + _mergeGroup.type
+				_error("Unsupported merge object type '" + _mergeGroup.type
 					+ "' in Zotero_Merge_Window.init()");
+				return;
 		}
 		
 		_mergeGroup.leftCaption = _io.dataIn.captions[0];
@@ -128,13 +129,8 @@ var Zotero_Merge_Window = new function () {
 			}
 		}
 		catch (e) {
-			Zotero.debug(e);
-			
-			var prompt = Components.classes["@mozilla.org/network/default-prompt;1"]
-							.createInstance(Components.interfaces.nsIPrompt);
-			prompt.alert(Zotero.getString('general.error'), e);
-			_wizard.getButton('cancel').click();
-			return false;
+			_error(e);
+			return;
 		}
 		
 		if (_mergeGroup.type == 'item') {
@@ -203,8 +199,9 @@ var Zotero_Merge_Window = new function () {
 	// Hack to support creator reconciliation via item view
 	function _updateChangedCreators() {
 		if (_mergeGroup.type != 'item') {
-			throw ("_updateChangedCreators called on non-item object in "
+			_error("_updateChangedCreators called on non-item object in "
 				+ "Zotero_Merge_Window._updateChangedCreators()");
+			return;
 		}
 		
 		if (_io.dataIn.changedCreators) {
@@ -228,4 +225,11 @@ var Zotero_Merge_Window = new function () {
 			}
 		}
 	}
+	
+	
+	function _error(e) {
+		Zotero.debug(e);
+		_io.error = e;
+		_wizard.getButton('cancel').click();
+	}
 }
diff --git a/chrome/content/zotero/xpcom/sync.js b/chrome/content/zotero/xpcom/sync.js
index 8db0954153..4ced787f9f 100644
--- a/chrome/content/zotero/xpcom/sync.js
+++ b/chrome/content/zotero/xpcom/sync.js
@@ -144,10 +144,6 @@ Zotero.Sync = new function() {
 		}
 		
 		// Last sync time is before start of log
-		Zotero.debug('==============');
-		Zotero.debug(lastSyncDate);
-		Zotero.debug(lastSyncDate + '');
-		Zotero.debug(syncLogStart);
 		if (lastSyncDate && new Date(syncLogStart * 1000) > lastSyncDate) {
 			return -1;
 		}
@@ -2668,9 +2664,8 @@ Zotero.Sync.Server.Data = new function() {
 				
 				var mergeData = _reconcile(type, toReconcile, remoteCreatorStore);
 				if (!mergeData) {
-					// TODO: throw?
 					Zotero.DB.rollbackTransaction();
-					return false;
+					throw ("Merge error");
 				}
 				_processMergeData(
 					syncSession,
@@ -3205,7 +3200,9 @@ Zotero.Sync.Server.Data = new function() {
 				   .getService(Components.interfaces.nsIWindowMediator);
 		var lastWin = wm.getMostRecentWindow("navigator:browser");
 		lastWin.openDialog('chrome://zotero/content/merge.xul', '', 'chrome,modal,centerscreen', io);
-		
+		if (io.error) {
+			throw (io.error);
+		}
 		return io.dataOut;
 	}