diff --git a/tools/doc.pl b/tools/doc.pl
index ff4503f..a81ce71 100755
--- a/tools/doc.pl
+++ b/tools/doc.pl
@@ -10,8 +10,8 @@ sub sentence {
     my $str = $_[0];
     $str =~ s/([^\.])$/\1./g;
     $str =~ s/`(.+?)`/<code>\1<\/code>/g;
-    $str =~ s/\*\*\*(.+?)\*\*\*/<b><i>\1<\/i><\/b>/g;
-    $str =~ s/\*\*(.+?)\*\*/<b>\1<\/b>/g;
+    $str =~ s/\*{3}(.+?)\*{3}/<b><i>\1<\/i><\/b>/g;
+    $str =~ s/\*{2}(.+?)\*{2}/<b>\1<\/b>/g;
     $str =~ s/\*(.+?)\*/<i>\1<\/i>/g;
     return $str;
 }