diff --git a/btrbk b/btrbk
index c653fbf..dc7db43 100755
--- a/btrbk
+++ b/btrbk
@@ -65,7 +65,7 @@ my $timestamp_postfix_match = qr/\.(?<YYYY>[0-9]{4})(?<MM>[0-9]{2})(?<DD>[0-9]{2
 my $raw_postfix_match = qr/--(?<received_uuid>$uuid_match)(\@(?<parent_uuid>$uuid_match))?\.btrfs?(\.(?<compress>(gz|bz2|xz)))?(\.(?<encrypt>gpg))?/;  # matches ".btrfs_<received_uuid>[@<parent_uuid>][.gz|bz2|xz][.gpg]"
 my $group_match = qr/[a-zA-Z0-9_:-]+/;
 my $ssh_cipher_match = qr/[a-z0-9][a-z0-9@.-]+/;
-my $safe_cmd_match = $file_match;  # good enough for our purpose
+my $safe_cmd_match = qr/[0-9a-zA-Z_@=\+\-\.\/]+/;  # $file_match plus '=': good enough for our purpose
 
 my %day_of_week_map = ( monday => 1, tuesday => 2, wednesday => 3, thursday => 4, friday => 5, saturday => 6, sunday => 7 );