diff --git a/tractags/model.py b/tractags/model.py
--- a/tractags/model.py
+++ b/tractags/model.py
@@ -62,8 +62,15 @@
         self._upgrade_db(db)

     def _need_migration(self, db):
+        cursor = db.cursor()
+        if self.env.config.get('trac', 'database').startswith('postgres'):
+            cursor.execute("SELECT relname FROM pg_class WHERE relname = 'wiki_namespace'")
+            if cursor.fetchone() is not None:
+                self.env.log.debug("tractags needs to migrate old data")
+                return True
+            else:
+                return False
         try:
-            cursor = db.cursor()
             cursor.execute("SELECT COUNT(*) FROM wiki_namespace")
             cursor.fetchone()
             self.env.log.debug("tractags needs to migrate old data")