diff --git a/pkgs/development/interpreters/tcl/mk-tcl-derivation.nix b/pkgs/development/interpreters/tcl/mk-tcl-derivation.nix
index aae8369cab20..3a61d556837f 100644
--- a/pkgs/development/interpreters/tcl/mk-tcl-derivation.nix
+++ b/pkgs/development/interpreters/tcl/mk-tcl-derivation.nix
@@ -57,7 +57,7 @@ let
         ];
         propagatedBuildInputs = propagatedBuildInputs ++ [ tcl ];
 
-        TCLSH = "${getBin tcl}/bin/tclsh";
+        env.TCLSH = "${getBin tcl}/bin/tclsh";
 
         # Run tests after install, at which point we've done all TCLLIBPATH setup
         doCheck = false;