diff --git a/pkgs/development/interpreters/python/pypy/prebuilt_2_7.nix b/pkgs/development/interpreters/python/pypy/prebuilt_2_7.nix
index fc8fdf79208c..e5893818407b 100644
--- a/pkgs/development/interpreters/python/pypy/prebuilt_2_7.nix
+++ b/pkgs/development/interpreters/python/pypy/prebuilt_2_7.nix
@@ -175,7 +175,7 @@ stdenv.mkDerivation {
     homepage = "http://pypy.org/";
     description = "Fast, compliant alternative implementation of the Python language (${pythonVersion})";
     license = licenses.mit;
-    platforms = lib.mapAttrsToList (arch: _: arch) downloadUrls;
+    platforms = lib.attrNames downloadUrls;
   };
 
 }