diff --git a/src/Database/Persist/Box/Internal.hs b/src/Database/Persist/Box/Internal.hs
index 78e1b12..1769d1c 100644
--- a/src/Database/Persist/Box/Internal.hs
+++ b/src/Database/Persist/Box/Internal.hs
@@ -177,7 +177,7 @@ createCellIfNeeded p = do
                     , " NOT NULL)"
                     ]
             in  rawExecute query []
-        [Single (_ :: a)] -> pure ()
+        [Single (_ :: String)] -> pure ()
         _ -> error "Multiple cell tables in sqlite_master"
 
 model :: QuasiQuoter