diff --git a/plugins/virus/clamdscan b/plugins/virus/clamdscan
index 3fb220c..808d307 100644
--- a/plugins/virus/clamdscan
+++ b/plugins/virus/clamdscan
@@ -323,21 +323,21 @@ sub is_too_big {
     return 0;
 }
 
-sub is_not_multipart {
+sub is_multipart {
     my $self = shift;
     my $transaction = shift || $self->qp->transaction;
 
-    return 1 if !$transaction->header;
+    return 0 if !$transaction->header;
 
     # Ignore non-multipart emails
-    my $content_type = $transaction->header->get('Content-Type') or return 1;
+    my $content_type = $transaction->header->get('Content-Type') or return 0;
     $content_type =~ s/\s/ /g;
     if ($content_type !~ m!\bmultipart/.*\bboundary="?([^"]+)!i) {
         $self->log(LOGNOTICE, "skip, not multipart");
-        return 1;
+        return 0;
     }
 
-    return 0;
+    return 1;
 }
 
 sub should_scan {
@@ -345,6 +345,6 @@ sub should_scan {
     my $tran = shift;
     return 0 if $self->is_too_big($tran);
     return 1 if $self->{_args}{scan_all};
-    return 0 if $self->is_not_multipart($tran);
+    return 0 if ! $self->is_multipart($tran);
     return 1;
 }
diff --git a/t/plugin_tests/virus/clamdscan b/t/plugin_tests/virus/clamdscan
index 0aa450f..b7b2344 100644
--- a/t/plugin_tests/virus/clamdscan
+++ b/t/plugin_tests/virus/clamdscan
@@ -21,7 +21,7 @@ sub register_tests {
     $self->register_test('test_get_filename', 1);
     $self->register_test('test_set_permission', 1);
     $self->register_test('test_is_too_big', 2);
-    $self->register_test('test_is_not_multipart', 2);
+    $self->register_test('test_is_multipart', 2);
     $self->register_test('test_should_scan',4);
 }
 
@@ -77,15 +77,15 @@ sub test_is_too_big {
     ok( $self->is_too_big( $tran ), "is_too_big 2");
 }
 
-sub test_is_not_multipart {
+sub test_is_multipart {
     my $self = shift;
     my $tran = Qpsmtpd::Transaction->new();
 
-    ok( $self->is_not_multipart($tran), "not_multipart 1" );
+    ok( ! $self->is_multipart($tran), "is_multipart 1" );
     $tran->header( Mail::Header->new( [
         'Content-Type: multipart/alternative; boundary="Jx3Wbb8BMHsO=_?:"'
     ] ) );
-    ok( ! $self->is_not_multipart($tran), "not_multipart 2" );
+    ok( $self->is_multipart($tran), "is_multipart 2" );
 }
 
 sub test_should_scan {