diff --git a/doc/cross-compilation.xml b/doc/cross-compilation.xml
index c7187d86d1b..3b90596bcc2 100644
--- a/doc/cross-compilation.xml
+++ b/doc/cross-compilation.xml
@@ -47,9 +47,13 @@
 
    <para>
     In Nixpkgs, these three platforms are defined as attribute sets under the
-    names <literal>buildPlatform</literal>, <literal>hostPlatform</literal>, and
-    <literal>targetPlatform</literal>. They are always defined as attributes in
-    the standard environment. That means one can access them like:
+    names <literal>buildPlatform</literal>, <literal>hostPlatform</literal>,
+    and <literal>targetPlatform</literal>. All three are always defined as
+    attributes in the standard environment, and at the top level. That means
+    one can get at them just like a dependency in a function that is imported
+    with <literal>callPackage</literal>:
+<programlisting>{ stdenv, buildPlatform, hostPlatform, fooDep, barDep, .. }: ...buildPlatform...</programlisting>
+    , or just off <varname>stdenv</varname>:
 <programlisting>{ stdenv, fooDep, barDep, .. }: ...stdenv.buildPlatform...</programlisting>
     .
    </para>
diff --git a/pkgs/top-level/stage.nix b/pkgs/top-level/stage.nix
index ff09fa5ad1f..06978d1067b 100644
--- a/pkgs/top-level/stage.nix
+++ b/pkgs/top-level/stage.nix
@@ -79,17 +79,11 @@ let
 
   # The old identifiers for cross-compiling. These should eventually be removed,
   # and the packages that rely on them refactored accordingly.
-  platformCompat = self: super: {
-    buildPlatform = lib.warn
-      "top-level `buildPlatform` is deprecated since 18.09. Please use `stdenv.buildPlatform`."
-      super.stdenv.buildPlatform;
-    hostPlatform = lib.warn
-      "top-level `hostPlatform` is deprecated since 18.09. Please use `stdenv.hostPlatform`."
-      super.stdenv.hostPlatform;
-    targetPlatform = lib.warn
-      "top-level `targetPlatform` is deprecated since 18.09. Please use `stdenv.targetPlatform`."
-      super.stdenv.targetPlatform;
-    inherit (super.stdenv.hostPlatform) system;
+  platformCompat = self: super: let
+    inherit (super.stdenv) buildPlatform hostPlatform targetPlatform;
+  in {
+    inherit buildPlatform hostPlatform targetPlatform;
+    inherit (buildPlatform) system;
   };
 
   splice = self: super: import ./splice.nix lib self (buildPackages != null);