diff --git a/scripts/nix-build.in b/scripts/nix-build.in
index fe22058f6..8b66e38a9 100755
--- a/scripts/nix-build.in
+++ b/scripts/nix-build.in
@@ -185,7 +185,7 @@ foreach my $expr (@exprs) {
         # Set the environment.
         if ($pure) {
             foreach my $name (keys %ENV) {
-                next if $name eq "HOME" || $name eq "USER" || $name eq "LOGNAME" || $name eq "DISPLAY" || $name eq "PATH" || $name eq "TERM";
+                next if $name eq "HOME" || $name eq "USER" || $name eq "LOGNAME" || $name eq "DISPLAY" || $name eq "PATH" || $name eq "TERM" || $name eq "IN_NIX_SHELL";
                 delete $ENV{$name};
             }
             # NixOS hack: prevent /etc/bashrc from sourcing /etc/profile.