diff --git a/pkgs/build-support/buildenv/builder.pl b/pkgs/build-support/buildenv/builder.pl
index 678f5a3fe9e6..7cc37d156735 100755
--- a/pkgs/build-support/buildenv/builder.pl
+++ b/pkgs/build-support/buildenv/builder.pl
@@ -141,12 +141,11 @@ sub addPkg {
     my $propagatedFN = "$pkgDir/nix-support/propagated-user-env-packages";
     if (-e $propagatedFN) {
         open PROP, "<$propagatedFN" or die;
-        my $propagated = <PROP>;
-        close PROP;
-        my @propagated = split ' ', $propagated;
-        foreach my $p (@propagated) {
+        while (my $p = <PROP>) {
+            chomp $p;
             $postponed{$p} = 1 unless defined $done{$p};
         }
+        close PROP;
     }
 }