diff --git a/plan2nix/Plan2Nix.hs b/plan2nix/Plan2Nix.hs
index ce27d23..d4b284f 100644
--- a/plan2nix/Plan2Nix.hs
+++ b/plan2nix/Plan2Nix.hs
@@ -106,7 +106,8 @@ plan2nix args (Plan { packages, extras, compilerVersion, compilerPackages }) = d
                return $ fromString pkg $= mkPath False nix
     _ -> return []
   let flags = concatMap (\case
-          (name, Just (Package v r flags _)) -> flags2nix name flags) $ Map.toList extras
+          (name, Just (Package _v _r f _)) -> flags2nix name f
+          _ -> []) $ Map.toList extras
 
   return $ mkNonRecSet [
     "pkgs" $= ("hackage" ==> mkNonRecSet (
@@ -119,7 +120,7 @@ plan2nix args (Plan { packages, extras, compilerVersion, compilerPackages }) = d
       ]))
     , "extras" $= ("hackage" ==> mkNonRecSet [ "packages" $= extrasNix ])
     , "modules" $= mkList [
-        mkNonRecSet [ "packages" $= mkNonRecSet flags ]
+        mkParamset [("lib", Nothing)] True ==> mkNonRecSet [ "packages" $= mkNonRecSet flags ]
       ]
     ]
  where
@@ -166,7 +167,9 @@ plan2nix args (Plan { packages, extras, compilerVersion, compilerPackages }) = d
 flags2nix :: Text -> HashMap Text Bool -> [Binding NExpr]
 flags2nix pkgName pkgFlags =
   [ quoted pkgName $= mkNonRecSet
-    [ "flags" $= mkNonRecSet [ quoted flag $= mkBool val
+    -- `mkOverride 900` is used here so that the default values will be replaced (they are 1000).
+    -- Values without a priority are treated as 100 and will replace these ones.
+    [ "flags" $= mkNonRecSet [ quoted flag $= ("lib" @. "mkOverride" @@ mkInt 900 @@ mkBool val)
                              | (flag, val) <- Map.toList pkgFlags
                              ]
     ]
diff --git a/stack2nix/Stack2nix.hs b/stack2nix/Stack2nix.hs
index 24d23d8..60f9542 100644
--- a/stack2nix/Stack2nix.hs
+++ b/stack2nix/Stack2nix.hs
@@ -80,7 +80,7 @@ stack2nix args stack@(Stack resolver compiler pkgs pkgFlags ghcOpts) =
                       | (Just c) <- [compiler], let name = filter (`elem` ((['a'..'z']++['0'..'9']) :: [Char])) c]))
        , "resolver"  $= fromString (quoted resolver)
        , "modules" $= mkList [
-           mkNonRecSet [ "packages" $= mkNonRecSet flags ]
+           mkParamset [("lib", Nothing)] True ==> mkNonRecSet [ "packages" $= mkNonRecSet flags ]
          , mkNonRecSet [ "packages" $= mkNonRecSet ghcOptions ] ]
        ] ++ [
          "compiler" $= fromString (quoted c) | (Just c) <- [compiler]
@@ -112,7 +112,9 @@ extraDeps2nix pkgs =
 flags2nix :: PackageFlags -> [Binding NExpr]
 flags2nix pkgFlags =
   [ quoted pkgName $= mkNonRecSet
-    [ "flags" $= mkNonRecSet [ quoted flag $= mkBool val
+    -- `mkOverride 900` is used here so that the default values will be replaced (they are 1000).
+    -- Values without a priority are treated as 100 and will replace these ones.
+    [ "flags" $= mkNonRecSet [ quoted flag $= ("lib" @. "mkOverride" @@ mkInt 900 @@ mkBool val)
                              | (flag, val) <- HM.toList flags
                              ]
     ]