diff --git a/chrome/content/zotero/xpcom/schema.js b/chrome/content/zotero/xpcom/schema.js
index aaf735387..be1746cc9 100644
--- a/chrome/content/zotero/xpcom/schema.js
+++ b/chrome/content/zotero/xpcom/schema.js
@@ -1945,7 +1945,7 @@ Zotero.Schema = new function(){
 				
 				yield Zotero.DB.queryAsync("ALTER TABLE libraries ADD COLUMN version INT NOT NULL DEFAULT 0");
 				yield Zotero.DB.queryAsync("ALTER TABLE libraries ADD COLUMN lastsync INT NOT NULL DEFAULT 0");
-				yield Zotero.DB.queryAsync("CREATE TABLE syncCache (\n    libraryID INT NOT NULL,\n    key TEXT NOT NULL,\n    syncObjectTypeID INT NOT NULL,\n    version INT NOT NULL,\n    data TEXT,\n    PRIMARY KEY (libraryID, key, syncObjectTypeID),\n    FOREIGN KEY (libraryID) REFERENCES libraries(libraryID) ON DELETE CASCADE,\n    FOREIGN KEY (syncObjectTypeID) REFERENCES syncObjectTypes(syncObjectTypeID)\n)");
+				yield Zotero.DB.queryAsync("CREATE TABLE syncCache (\n    libraryID INT NOT NULL,\n    key TEXT NOT NULL,\n    syncObjectTypeID INT NOT NULL,\n    version INT NOT NULL,\n    data TEXT,\n    PRIMARY KEY (libraryID, key, syncObjectTypeID, version),\n    FOREIGN KEY (libraryID) REFERENCES libraries(libraryID) ON DELETE CASCADE,\n    FOREIGN KEY (syncObjectTypeID) REFERENCES syncObjectTypes(syncObjectTypeID)\n)");
 				
 				yield Zotero.DB.queryAsync("DROP TABLE translatorCache");
 				yield Zotero.DB.queryAsync("CREATE TABLE translatorCache (\n    fileName TEXT PRIMARY KEY,\n    metadataJSON TEXT,\n    lastModifiedTime INT\n);");
diff --git a/resource/schema/userdata.sql b/resource/schema/userdata.sql
index 1cd70833a..651abaf18 100644
--- a/resource/schema/userdata.sql
+++ b/resource/schema/userdata.sql
@@ -297,7 +297,7 @@ CREATE TABLE syncCache (
     syncObjectTypeID INT NOT NULL,
     version INT NOT NULL,
     data TEXT,
-    PRIMARY KEY (libraryID, key, syncObjectTypeID),
+    PRIMARY KEY (libraryID, key, syncObjectTypeID, version),
     FOREIGN KEY (libraryID) REFERENCES libraries(libraryID) ON DELETE CASCADE,
     FOREIGN KEY (syncObjectTypeID) REFERENCES syncObjectTypes(syncObjectTypeID)
 );