diff --git a/pkgs/top-level/release-lib.nix b/pkgs/top-level/release-lib.nix
index fba8429c9c7..5fe87711c01 100644
--- a/pkgs/top-level/release-lib.nix
+++ b/pkgs/top-level/release-lib.nix
@@ -46,21 +46,22 @@ rec {
      interested in the result of cross building a package. */
   crossMaintainers = [ maintainers.viric ];
 
+  forAllSupportedSystems = systems: f:
+    genAttrs (filter (x: elem x supportedSystems) systems) f;
 
   /* Build a package on the given set of platforms.  The function `f'
      is called for each supported platform with Nixpkgs for that
      platform as an argument .  We return an attribute set containing
      a derivation for each supported platform, i.e. ‘{ x86_64-linux =
      f pkgs_x86_64_linux; i686-linux = f pkgs_i686_linux; ... }’. */
-  testOn = systems: f: genAttrs
-    (filter (x: elem x supportedSystems) systems) (system: hydraJob' (f (pkgsFor system)));
+  testOn = systems: f: forAllSupportedSystems systems
+    (system: hydraJob' (f (pkgsFor system)));
 
 
   /* Similar to the testOn function, but with an additional
      'crossSystem' parameter for allPackages, defining the target
      platform for cross builds. */
-  testOnCross = crossSystem: systems: f: genAttrs
-    (filter (x: elem x supportedSystems) systems)
+  testOnCross = crossSystem: systems: f: forAllSupportedSystems systems
     (system: hydraJob' (f (allPackages { inherit system crossSystem; })));