diff --git a/services/tag2tagservice.php b/services/tag2tagservice.php
index 1c6392e..d3a4a77 100644
--- a/services/tag2tagservice.php
+++ b/services/tag2tagservice.php
@@ -17,7 +17,8 @@ class Tag2TagService {
 
     function addLinkedTags($tag1, $tag2, $relationType, $uId) {
 	if($tag1 == $tag2 || strlen($tag1) == 0 || strlen($tag2) == 0
-		|| ($relationType != ">" && $relationType != "=")) {
+		|| ($relationType != ">" && $relationType != "=")
+		|| ($this->existsLinkedTags($tag1, $tag2, $relationType, $uId))) {
 		return false;
 	}
 	$values = array('tag1' => $tag1, 'tag2' => $tag2, 'relationType'=> $relationType, 'uId'=> $uId);
diff --git a/tests/tag2TagTest.php b/tests/tag2TagTest.php
index f54537c..87dde52 100644
--- a/tests/tag2TagTest.php
+++ b/tests/tag2TagTest.php
@@ -264,6 +264,8 @@ class Tag2TagTest extends PHPUnit_Framework_TestCase
 	$tts = $this->tts;
 	$bs = $this->bs;
 
+	$tts->addLinkedTags('aa', 'bb', '>', 1);	
+
 	$tags = array('aa>bb>cc', 'dd');
 	$bs->addBookmark("web1.com", "B1", "description", "status", $tags, null, false, false, 1);
 	$tags = array('bb>gg', 'ee>ff');