diff --git a/perl/lib/Nix/Utils.pm b/perl/lib/Nix/Utils.pm
index bc180e2a55..78d3db5427 100644
--- a/perl/lib/Nix/Utils.pm
+++ b/perl/lib/Nix/Utils.pm
@@ -23,7 +23,7 @@ sub uniq {
 
 sub writeFile {
     my ($fn, $s) = @_;
-    open TMP, ">$fn" or die;
+    open TMP, ">$fn" or die "cannot create file `$fn': $!";
     print TMP "$s" or die;
     close TMP or die;
 }
@@ -31,7 +31,7 @@ sub writeFile {
 sub readFile {
     local $/ = undef;
     my ($fn) = @_;
-    open TMP, "<$fn" or die;
+    open TMP, "<$fn" or die "cannot open file `$fn': $!";
     my $s = <TMP>;
     close TMP or die;
     return $s;