diff --git a/nix/overlays.nix b/nix/overlays.nix
index 14a47ca5a..f5ef72cc0 100644
--- a/nix/overlays.nix
+++ b/nix/overlays.nix
@@ -2,25 +2,25 @@ self: super: {
   python27 = super.python27.override {
     packageOverrides = python-self: python-super: {
       # eliot is not part of nixpkgs at all at this time.
-      eliot = python-self.callPackage ./eliot.nix { };
+      eliot = python-self.pythonPackages.callPackage ./eliot.nix { };
 
       # NixOS autobahn package has trollius as a dependency, although
       # it is optional. Trollius is unmaintained and fails on CI.
-      autobahn = python-super.callPackage ./autobahn.nix { };
+      autobahn = python-super.pythonPackages.callPackage ./autobahn.nix { };
 
       # Porting to Python 3 is greatly aided by the future package.  A
       # slightly newer version than appears in nixos 19.09 is helpful.
-      future = python-super.callPackage ./future.nix { };
+      future = python-super.pythonPackages.callPackage ./future.nix { };
 
       # Need version of pyutil that supports Python 3. The version in 19.09
       # is too old.
-      pyutil = python-super.callPackage ./pyutil.nix { };
+      pyutil = python-super.pythonPackages.callPackage ./pyutil.nix { };
 
       # Need a newer version of Twisted, too.
-      twisted = python-super.callPackage ./twisted.nix { };
+      twisted = python-super.pythonPackages.callPackage ./twisted.nix { };
 
       # collections-extended is not part of nixpkgs at this time.
-      collections-extended = python-super.callPackage ./collections-extended.nix { };
+      collections-extended = python-super.pythonPackages.callPackage ./collections-extended.nix { };
     };
   };
 }