diff --git a/pkgs/build-support/mkshell/default.nix b/pkgs/build-support/mkshell/default.nix
index e7552f434848..39b02a47141a 100644
--- a/pkgs/build-support/mkshell/default.nix
+++ b/pkgs/build-support/mkshell/default.nix
@@ -44,12 +44,13 @@ stdenv.mkDerivation ({
   phases = [ "buildPhase" ];
 
   buildPhase = ''
-    echo "------------------------------------------------------------" >>$out
-    echo " WARNING: the existence of this path is not guaranteed." >>$out
-    echo " It is an internal implementation detail for pkgs.mkShell."   >>$out
-    echo "------------------------------------------------------------" >>$out
-    echo >> $out
-    # Record all build inputs as runtime dependencies
-    export >> $out
+    { echo "------------------------------------------------------------";
+      echo " WARNING: the existence of this path is not guaranteed.";
+      echo " It is an internal implementation detail for pkgs.mkShell.";
+      echo "------------------------------------------------------------";
+      echo;
+      # Record all build inputs as runtime dependencies
+      export;
+    } >> "$out"
   '';
 } // rest)