diff --git a/chrome/content/zotero/xpcom/sync/syncRunner.js b/chrome/content/zotero/xpcom/sync/syncRunner.js
index 912a3fdc4..da99dd45a 100644
--- a/chrome/content/zotero/xpcom/sync/syncRunner.js
+++ b/chrome/content/zotero/xpcom/sync/syncRunner.js
@@ -139,6 +139,19 @@ Zotero.Sync.Runner_Module = function (options = {}) {
 			
 			this.updateIcons('animate');
 			
+			// purgeDataObjects() starts a transaction, so if there's an active one then show a
+			// nice message and wait until there's not. Another transaction could still start
+			// before purgeDataObjects() and result in a wait timeout, but this should reduce the
+			// frequency of that.
+			while (Zotero.DB.inTransaction()) {
+				this.setSyncStatus(Zotero.getString('sync.status.waiting'));
+				Zotero.debug("Transaction in progress -- waiting to sync");
+				yield Zotero.DB.waitForTransaction('sync');
+				_stopCheck();
+			}
+			
+			this.setSyncStatus(Zotero.getString('sync.status.preparing'));
+			
 			// Purge deleted objects so they don't cause sync errors (e.g., long tags)
 			yield Zotero.purgeDataObjects(true);
 			
diff --git a/chrome/locale/en-US/zotero/zotero.properties b/chrome/locale/en-US/zotero/zotero.properties
index 209e43926..4ec928bba 100644
--- a/chrome/locale/en-US/zotero/zotero.properties
+++ b/chrome/locale/en-US/zotero/zotero.properties
@@ -952,6 +952,8 @@ sync.conflict.chooseThisVersion			= Choose this version
 
 sync.status.notYetSynced			= Not yet synced
 sync.status.lastSync				= Last sync:
+sync.status.waiting                = Waiting for other operations to finish
+sync.status.preparing              = Preparing sync
 sync.status.loggingIn				= Logging in to sync server
 sync.status.gettingUpdatedData		= Getting updated data from sync server
 sync.status.processingUpdatedData	= Processing updated data from sync server