diff --git a/src/Database/Esqueleto/Experimental.hs b/src/Database/Esqueleto/Experimental.hs
index a96d1d5..e9ddd9f 100644
--- a/src/Database/Esqueleto/Experimental.hs
+++ b/src/Database/Esqueleto/Experimental.hs
@@ -53,8 +53,6 @@ module Database.Esqueleto.Experimental
     , with
     , withRecursive
 
-    , agg
-
       -- ** Internals
     , From(..)
     , ToMaybe(..)
diff --git a/src/Database/Esqueleto/Experimental/Aggregates.hs b/src/Database/Esqueleto/Experimental/Aggregates.hs
index 0968d4c..315908c 100644
--- a/src/Database/Esqueleto/Experimental/Aggregates.hs
+++ b/src/Database/Esqueleto/Experimental/Aggregates.hs
@@ -16,11 +16,13 @@ module Database.Esqueleto.Experimental.Aggregates
 import Control.Monad.IO.Class
 import qualified Control.Monad.Trans.Writer as W
 import Data.Coerce (Coercible, coerce)
+import Data.Proxy
 import Database.Esqueleto.Internal.Internal
        ( GroupByClause(..)
        , SideData(..)
        , SqlExpr(..)
        , SqlQuery(..)
+       , SqlQueryHaving(..)
        , SqlSelect(..)
        , ToSomeValues(..)
        , noMeta
@@ -53,8 +55,16 @@ instance SqlExprEntity SqlExpr where
     (^.) = (I.^.)
     (?.) = (I.?.)
 
-newtype SqlAggregate a = SqlAggregate { agg :: SqlExpr a }
+newtype SqlAggregate a = SqlAggregate { unsafeSqlAggregate :: SqlExpr a }
 deriving via SqlExpr instance SqlExprEntity SqlAggregate
+instance forall a. PersistField a => SqlSelect (SqlAggregate a) a where
+    sqlSelectCols info (SqlAggregate e) = sqlSelectCols info e
+    sqlSelectColCount = const 1
+    sqlSelectProcessRow _ = sqlSelectProcessRow (Proxy :: Proxy (SqlExpr a))
+instance SqlQueryHaving (SqlAggregate Bool) where
+    having expr = Q $ W.tell mempty { sdHavingClause = I.Where (coerce expr) }
+instance SqlQueryHaving (SqlAggregate (Maybe Bool)) where
+    having expr = Q $ W.tell mempty { sdHavingClause = I.Where (coerce expr) }
 
 test :: (PersistEntity ent, PersistField a, PersistField b, PersistField c)
      => SqlExpr (Maybe (Entity ent))
diff --git a/src/Database/Esqueleto/Experimental/WindowFunctions.hs b/src/Database/Esqueleto/Experimental/WindowFunctions.hs
index 5f5b99f..2b6c441 100644
--- a/src/Database/Esqueleto/Experimental/WindowFunctions.hs
+++ b/src/Database/Esqueleto/Experimental/WindowFunctions.hs
@@ -62,7 +62,7 @@ example =
         <> orderBy_ [asc (val @Int64 10)]
         )
 
-data NeedsWindow a
+example2 = countRows_ @Int64 `over_` ()
 
 lag :: SqlExpr (Value a) -> WindowExpr a
 lag v = lag_ v Nothing Nothing
@@ -254,7 +254,7 @@ currentRow :: FrameRange
 currentRow = FrameRangeCurrentRow
 
 class Over expr where
-    over_ :: RenderWindow window => expr a -> window -> SqlExpr (WindowedValue a)
+    over_ :: RenderWindow window => expr a -> window -> SqlAggregate (WindowedValue a)
 
 data WindowedValue a = WindowedValue { unWindowedValue :: a }
 instance PersistField a => SqlSelect (SqlExpr (WindowedValue a)) (WindowedValue a) where
@@ -266,7 +266,7 @@ instance PersistField a => SqlSelect (SqlExpr (WindowedValue a)) (WindowedValue
 
 newtype WindowExpr a = WindowExpr { unsafeWindowExpr :: SqlExpr a }
 instance Over WindowExpr where
-    (WindowExpr (ERaw _ f)) `over_` window = ERaw noMeta $ \p info ->
+    (WindowExpr (ERaw _ f)) `over_` window = SqlAggregate $ ERaw noMeta $ \p info ->
         let (b, v) = f Never info
             (w, vw) = renderWindow info window
         in (parensM p $ b <> " OVER " <> parens w , v <> vw)
diff --git a/src/Database/Esqueleto/Internal/Internal.hs b/src/Database/Esqueleto/Internal/Internal.hs
index dbb61f3..98bb376 100644
--- a/src/Database/Esqueleto/Internal/Internal.hs
+++ b/src/Database/Esqueleto/Internal/Internal.hs
@@ -377,11 +377,16 @@ distinctOnOrderBy exprs act =
 rand :: SqlExpr OrderBy
 rand = ERaw noMeta $ \_ _ -> ("RANDOM()", []) 
 
--- | @HAVING@.
---
--- @since 1.2.2
-having :: SqlExpr Bool -> SqlQuery ()
-having expr = Q $ W.tell mempty { sdHavingClause = Where expr }
+class SqlQueryHaving expr where
+    -- | @HAVING@.
+    --
+    -- @since 1.2.2
+    having :: expr -> SqlQuery ()
+
+instance SqlQueryHaving (SqlExpr Bool) where
+    having expr = Q $ W.tell mempty { sdHavingClause = Where expr }
+instance SqlQueryHaving (SqlExpr (Maybe Bool)) where
+    having expr = Q $ W.tell mempty { sdHavingClause = Where (coerce expr) }
 
 -- | Add a locking clause to the query.  Please read
 -- 'LockingKind' documentation and your RDBMS manual.