diff --git a/src/Database/Esqueleto/Internal/Language.hs b/src/Database/Esqueleto/Internal/Language.hs
index ac398b2..48ad25b 100644
--- a/src/Database/Esqueleto/Internal/Language.hs
+++ b/src/Database/Esqueleto/Internal/Language.hs
@@ -237,12 +237,12 @@ class (Functor query, Applicative query, Monad query) =>
   (*.)  :: PersistField a => expr (Value a) -> expr (Value a) -> expr (Value a)
 
 
-  random_  :: PersistField a => expr (Value a)
-  round_   :: (PersistField a, PersistField b) => expr (Value a) -> expr (Value b)
-  ceiling_ :: (PersistField a, PersistField b) => expr (Value a) -> expr (Value b)
-  floor_   :: (PersistField a, PersistField b) => expr (Value a) -> expr (Value b)
+  random_  :: (PersistField a, Num a) => expr (Value a)
+  round_   :: (PersistField a, Num a, PersistField b, Num b) => expr (Value a) -> expr (Value b)
+  ceiling_ :: (PersistField a, Num a, PersistField b, Num b) => expr (Value a) -> expr (Value b)
+  floor_   :: (PersistField a, Num a, PersistField b, Num b) => expr (Value a) -> expr (Value b)
 
-  sum_     :: (PersistField a) => expr (Value a) -> expr (Value (Maybe a))
+  sum_     :: (PersistField a, PersistField b) => expr (Value a) -> expr (Value (Maybe b))
   min_     :: (PersistField a) => expr (Value a) -> expr (Value (Maybe a))
   max_     :: (PersistField a) => expr (Value a) -> expr (Value (Maybe a))
   avg_     :: (PersistField a, PersistField b) => expr (Value a) -> expr (Value (Maybe b))
diff --git a/test/Test.hs b/test/Test.hs
index b084802..35636ae 100644
--- a/test/Test.hs
+++ b/test/Test.hs
@@ -323,7 +323,13 @@ main = do
           ret <- select $
                  from $ \p->
                  return $ joinV $ sum_ (p ^. PersonAge)
+#if   defined(WITH_POSTGRESQL)
+          liftIO $ ret `shouldBe` [ Value $ Just (36 + 17 + 17 :: Rational ) ]
+#elif defined(WITH_MYSQL)
+          liftIO $ ret `shouldBe` [ Value $ Just (36 + 17 + 17 :: Double ) ]
+#else
           liftIO $ ret `shouldBe` [ Value $ Just (36 + 17 + 17 :: Int) ]
+#endif
 
       it "works with avg_" $
         run $ do