diff --git a/pkgs/stdenv/cross/default.nix b/pkgs/stdenv/cross/default.nix
index daa9f66615c..a6063049a3a 100644
--- a/pkgs/stdenv/cross/default.nix
+++ b/pkgs/stdenv/cross/default.nix
@@ -1,11 +1,14 @@
 { lib
-, localSystem, crossSystem, config, overlays
+, localSystem, crossSystem, config, overlays, crossOverlays ? []
 }:
 
 let
   bootStages = import ../. {
     inherit lib localSystem overlays;
-    crossSystem = null;
+
+    crossSystem = localSystem;
+    crossOverlays = [];
+
     # Ignore custom stdenvs when cross compiling for compatability
     config = builtins.removeAttrs config [ "replaceStdenv" ];
   };
@@ -33,7 +36,8 @@ in lib.init bootStages ++ [
 
   # Run Packages
   (buildPackages: {
-    inherit config overlays;
+    inherit config;
+    overlays = overlays ++ crossOverlays;
     selfBuild = false;
     stdenv = buildPackages.stdenv.override (old: rec {
       buildPlatform = localSystem;
@@ -48,7 +52,7 @@ in lib.init bootStages ++ [
 
       cc = if crossSystem.useiOSPrebuilt or false
              then buildPackages.darwin.iosSdkPkgs.clang
-           else if crossSystem.useAndroidPrebuilt
+           else if crossSystem.useAndroidPrebuilt or false
              then buildPackages.androidenv."androidndkPkgs_${crossSystem.ndkVer}".gcc
            else buildPackages.gcc;
 
@@ -56,6 +60,7 @@ in lib.init bootStages ++ [
         ++ lib.optionals
              (hostPlatform.isLinux && !buildPlatform.isLinux)
              [ buildPackages.patchelf buildPackages.paxctl ]
+        ++ lib.optional hostPlatform.isDarwin buildPackages.clang
         ++ lib.optional
              (let f = p: !p.isx86 || p.libc == "musl"; in f hostPlatform && !(f buildPlatform))
              buildPackages.updateAutotoolsGnuConfigScriptsHook
diff --git a/pkgs/stdenv/custom/default.nix b/pkgs/stdenv/custom/default.nix
index b6ea8685f8e..e86face9519 100644
--- a/pkgs/stdenv/custom/default.nix
+++ b/pkgs/stdenv/custom/default.nix
@@ -2,7 +2,7 @@
 , localSystem, crossSystem, config, overlays
 }:
 
-assert crossSystem == null;
+assert crossSystem == localSystem;
 
 let
   bootStages = import ../. {
diff --git a/pkgs/stdenv/darwin/default.nix b/pkgs/stdenv/darwin/default.nix
index 5fb410b64eb..b7d8e3ba523 100644
--- a/pkgs/stdenv/darwin/default.nix
+++ b/pkgs/stdenv/darwin/default.nix
@@ -1,5 +1,5 @@
 { lib
-, localSystem, crossSystem, config, overlays
+, localSystem, crossSystem, config, overlays, crossOverlays ? []
 
 # Allow passing in bootstrap files directly so we can test the stdenv bootstrap process when changing the bootstrap tools
 , bootstrapFiles ? let
@@ -16,7 +16,7 @@
   }
 }:
 
-assert crossSystem == null;
+assert crossSystem == localSystem;
 
 let
   inherit (localSystem) system platform;
diff --git a/pkgs/stdenv/default.nix b/pkgs/stdenv/default.nix
index 210e0439c0b..c0bbe24e521 100644
--- a/pkgs/stdenv/default.nix
+++ b/pkgs/stdenv/default.nix
@@ -7,7 +7,7 @@
 { # Args just for stdenvs' usage
   lib
   # Args to pass on to the pkgset builder, too
-, localSystem, crossSystem, config, overlays
+, localSystem, crossSystem, config, overlays, crossOverlays ? []
 } @ args:
 
 let
@@ -36,7 +36,7 @@ let
 
   # Select the appropriate stages for the platform `system'.
 in
-  if crossSystem != null then stagesCross
+  if crossSystem != localSystem || crossOverlays != [] then stagesCross
   else if config ? replaceStdenv then stagesCustom
   else { # switch
     "i686-linux" = stagesLinux;
diff --git a/pkgs/stdenv/freebsd/default.nix b/pkgs/stdenv/freebsd/default.nix
index b3a6cedad84..dbb4a056455 100644
--- a/pkgs/stdenv/freebsd/default.nix
+++ b/pkgs/stdenv/freebsd/default.nix
@@ -2,7 +2,7 @@
 , localSystem, crossSystem, config, overlays
 }:
 
-assert crossSystem == null;
+assert crossSystem == localSystem;
 let inherit (localSystem) system; in
 
 
diff --git a/pkgs/stdenv/linux/default.nix b/pkgs/stdenv/linux/default.nix
index 978beea692c..6d793999d90 100644
--- a/pkgs/stdenv/linux/default.nix
+++ b/pkgs/stdenv/linux/default.nix
@@ -4,7 +4,7 @@
 # compiler and linker that do not search in default locations,
 # ensuring purity of components produced by it.
 { lib
-, localSystem, crossSystem, config, overlays
+, localSystem, crossSystem, config, overlays, crossOverlays ? []
 
 , bootstrapFiles ?
   let table = {
@@ -32,7 +32,7 @@
   in files
 }:
 
-assert crossSystem == null;
+assert crossSystem == localSystem;
 
 let
   inherit (localSystem) system platform;
diff --git a/pkgs/stdenv/native/default.nix b/pkgs/stdenv/native/default.nix
index 37795b11f6d..810cf16301f 100644
--- a/pkgs/stdenv/native/default.nix
+++ b/pkgs/stdenv/native/default.nix
@@ -2,7 +2,7 @@
 , localSystem, crossSystem, config, overlays
 }:
 
-assert crossSystem == null;
+assert crossSystem == localSystem;
 
 let
   inherit (localSystem) system;
diff --git a/pkgs/stdenv/nix/default.nix b/pkgs/stdenv/nix/default.nix
index ffff8bdf51d..a8311f49609 100644
--- a/pkgs/stdenv/nix/default.nix
+++ b/pkgs/stdenv/nix/default.nix
@@ -1,10 +1,10 @@
 { lib
-, crossSystem, config, overlays
+, crossSystem, localSystem, config, overlays
 , bootStages
 , ...
 }:
 
-assert crossSystem == null;
+assert crossSystem == localSystem;
 
 bootStages ++ [
   (prevStage: {
diff --git a/pkgs/top-level/default.nix b/pkgs/top-level/default.nix
index da7fc1bed34..dcd443a1c29 100644
--- a/pkgs/top-level/default.nix
+++ b/pkgs/top-level/default.nix
@@ -22,9 +22,8 @@
   # `*Platform`s.
   localSystem
 
-, # The system packages will ultimately be run on. Null if the two should be the
-  # same.
-  crossSystem ? null
+, # The system packages will ultimately be run on.
+  crossSystem ? localSystem
 
 , # Allow a configuration attribute set to be passed in as an argument.
   config ? {}
@@ -32,6 +31,9 @@
 , # List of overlays layers used to extend Nixpkgs.
   overlays ? []
 
+, # List of overlays to apply to target packages only.
+  crossOverlays ? []
+
 , # A function booting the final package set for a specific standard
   # environment. See below for the arguments given to that function, the type of
   # list it returns.
@@ -61,7 +63,8 @@ in let
     builtins.intersectAttrs { platform = null; } config
     // args.localSystem);
 
-  crossSystem = lib.mapNullable lib.systems.elaborate crossSystem0;
+  crossSystem = if crossSystem0 == null then localSystem
+                else lib.systems.elaborate crossSystem0;
 
   # A few packages make a new package set to draw their dependencies from.
   # (Currently to get a cross tool chain, or forced-i686 package.) Rather than
@@ -91,7 +94,7 @@ in let
   boot = import ../stdenv/booter.nix { inherit lib allPackages; };
 
   stages = stdenvStages {
-    inherit lib localSystem crossSystem config overlays;
+    inherit lib localSystem crossSystem config overlays crossOverlays;
   };
 
   pkgs = boot stages;