diff --git a/lib/Qpsmtpd/DB/File/DBM.pm b/lib/Qpsmtpd/DB/File/DBM.pm
index 6126a1d..7a30c5a 100644
--- a/lib/Qpsmtpd/DB/File/DBM.pm
+++ b/lib/Qpsmtpd/DB/File/DBM.pm
@@ -180,9 +180,13 @@ sub flush {
 }
 
 sub dir {
-    my ( $self, @arg ) = @_;
-    return $self->{dir} if $self->{dir} and ! @arg;
-    for my $d ( $self->candidate_dirs(@arg) ) {
+    my ( $self, $dir ) = @_;
+    if ( $dir ) {
+        die "Cannot use DB directory '$dir'\n" if !$self->validate_dir($dir);
+        return $self->{dir} = $dir;
+    }
+    return $self->{dir} if $self->{dir};
+    for my $d ( $self->candidate_dirs ) {
         next if ! $self->validate_dir($d);
         return $self->{dir} = $d; # first match wins
     }
diff --git a/plugins/greylisting b/plugins/greylisting
index 72b04f2..3c872a3 100644
--- a/plugins/greylisting
+++ b/plugins/greylisting
@@ -266,12 +266,17 @@ sub init_dbm {
         name  => 'greylist',
         class => 'Qpsmtpd::DB::File::DBM'
     );
-    my $cdir = $self->{_args}{db_dir};
-    $cdir = $1 if $cdir and $cdir =~ m{^([-a-zA-Z0-9./_]+)$};
-    # greylisting-specific hints for where to store the greylist DB
-    my $db_dir = $self->db->dir( $cdir, '/var/lib/qpsmtpd/greylisting' );
     $self->db->nfs_locking( $self->{_args}{nfslock} );
 
+    # Add to the default list of possible DB directories
+    $self->db->candidate_dirs('/var/lib/qpsmtpd/greylisting');
+    if ( my $dir_arg = $self->{_args}{db_dir} ) {
+        # user-supplied db dir
+        $dir_arg = $1 if $dir_arg =~ m{^([-a-zA-Z0-9./_]+)$};
+        $self->db->dir($dir_arg);
+    }
+    my $db_dir = $self->db->dir;
+
     # Work around old DBM filename
     my $oldname = 'denysoft_greylist';
     if ( ! -f "$db_dir/greylist.dbm" && -f "$db_dir/$oldname.dbm" ) {
diff --git a/t/qpsmtpd-db-file-dbm.t b/t/qpsmtpd-db-file-dbm.t
index c9e471d..65e1eb0 100644
--- a/t/qpsmtpd-db-file-dbm.t
+++ b/t/qpsmtpd-db-file-dbm.t
@@ -137,11 +137,17 @@ sub __validate_dir {
 sub __dir {
     my $db2 = Qpsmtpd::DB::File::DBM->new( name => 'dirtest' );
     is( $db2->dir(), 't/config', 'default directory' );
-    is( $db2->dir('_invalid','t/Test'), 't/Test', 'skip invalid candidate dirs' );
+    delete $db2->{dir};
+    $db2->candidate_dirs('_invalid','t/Test');
+    is( $db2->dir, 't/Test', 'skip invalid candidate dirs' );
     $db2->{dir} = '_cached';
     is( $db2->dir(), '_cached', 'cached directory' );
     is( $db2->dir('t/Test'), 't/Test', 'passing candidate dirs resets cache' );
-    is( $db2->dir('_invalid'), 't/config', 'invalid candidate dirs reverts to default' );
+    delete $db2->{dir};
+    $db2->candidate_dirs('_invalid');
+    is( $db2->dir, 't/config', 'invalid candidate dirs reverts to default' );
+    eval { $db2->dir('_invalid'); };
+    is( $@, "Cannot use DB directory '_invalid'\n", 'die on invalid dir' );
 }
 
 sub __untie_gotcha {