diff --git a/pkgs/development/python-modules/pypdf3/default.nix b/pkgs/development/python-modules/pypdf3/default.nix
index 78b230965674..2b44c409778e 100644
--- a/pkgs/development/python-modules/pypdf3/default.nix
+++ b/pkgs/development/python-modules/pypdf3/default.nix
@@ -18,7 +18,7 @@ buildPythonPackage (finalAttrs: {
     hash = "sha256-yUbzJzQZ43JY415yJz9JkEqxVyPYenYcERXvmXmfjF8=";
   };
 
-  LC_ALL = "en_US.UTF-8";
+  env.LC_ALL = "en_US.UTF-8";
   buildInputs = [ glibcLocales ];
 
   checkPhase = ''