diff --git a/lib/customisation.nix b/lib/customisation.nix
index 37a7951896b0e..ae507807b4d9e 100644
--- a/lib/customisation.nix
+++ b/lib/customisation.nix
@@ -231,6 +231,7 @@ rec {
       } // keep self;
       self = f self // {
         newScope = scope: newScope (spliced // scope);
+        makeScopeWithSplicing = makeScopeWithSplicing splicePackages self.newScope;
         callPackage = newScope spliced; # == self.newScope {};
         # N.B. the other stages of the package set spliced in are *not*
         # overridden.
diff --git a/pkgs/development/interpreters/python/default.nix b/pkgs/development/interpreters/python/default.nix
index 2f350738238e4..e8043325c2f0d 100644
--- a/pkgs/development/interpreters/python/default.nix
+++ b/pkgs/development/interpreters/python/default.nix
@@ -69,9 +69,7 @@ with pkgs;
               recursivePthLoader
             ;
           };
-        in lib.makeScopeWithSplicing
-          pkgs.splicePackages
-          pkgs.newScope
+        in pkgs.makeScopeWithSplicing
           otherSplices
           keep
           (lib.extends overrides pythonPackagesFun))
diff --git a/pkgs/top-level/splice.nix b/pkgs/top-level/splice.nix
index a093442d3698c..fb3c5d5317057 100644
--- a/pkgs/top-level/splice.nix
+++ b/pkgs/top-level/splice.nix
@@ -131,6 +131,17 @@ in
 
   newScope = extra: lib.callPackageWith (splicedPackagesWithXorg // extra);
 
+  makeScopeWithSplicing = lib.makeScopeWithSplicing splicePackages pkgs.newScope;
+
+  topProjectedSpliced = attr: {
+    selfBuildBuild   = pkgs.pkgsBuildBuild.${attr};
+    selfBuildHost    = pkgs.pkgsBuildHost.${attr};
+    selfBuildTarget  = pkgs.pkgsBuildTarget.${attr};
+    selfHostHost     = pkgs.pkgsHostHost.${attr};
+    selfHostTarget   = pkgs.pkgsHostTarget.${attr};
+    selfTargetTarget = pkgs.pkgsTargetTarget.${attr} or {};
+  };
+
   # Haskell package sets need this because they reimplement their own
   # `newScope`.
   __splicedPackages = splicedPackages // { recurseForDerivations = false; };