diff --git a/pkgs/stdenv/default.nix b/pkgs/stdenv/default.nix
index 98aefc2bf568..53f63245c919 100644
--- a/pkgs/stdenv/default.nix
+++ b/pkgs/stdenv/default.nix
@@ -43,7 +43,7 @@ in
 # Select the appropriate stages for the platform `system'.
 if crossSystem != localSystem || crossOverlays != [ ] then
   stagesCross
-else if config.replaceStdenv != null then
+else if (config.replaceStdenv or null) != null then
   stagesCustom
 else if localSystem.isLinux then
   stagesLinux