diff --git a/src/SemanticScuttle/Service/Bookmark.php b/src/SemanticScuttle/Service/Bookmark.php
index b0ffbac..5842390 100644
--- a/src/SemanticScuttle/Service/Bookmark.php
+++ b/src/SemanticScuttle/Service/Bookmark.php
@@ -236,10 +236,21 @@ class SemanticScuttle_Service_Bookmark extends SemanticScuttle_DbService
 
 
 
-    function bookmarkExists($address = false, $uid = NULL)
+    /**
+     * Checks if a bookmark for the given URL exists
+     * already
+     *
+     * @param string  $address URL of bookmark to check
+     * @param integer $uid     User id the bookmark has to belong to.
+     *                         null for all users
+     *
+     * @return boolean True when the bookmark with the given URL
+     *                 exists for the user, false if not.
+     */
+    function bookmarkExists($address = false, $uid = null)
     {
         if (!$address) {
-            return;
+            return false;
         }
 
         $address = $this->normalize($address);
diff --git a/tests/BookmarkTest.php b/tests/BookmarkTest.php
index caee84b..7940d8d 100644
--- a/tests/BookmarkTest.php
+++ b/tests/BookmarkTest.php
@@ -134,6 +134,106 @@ class BookmarkTest extends TestBase
 
 
 
+    /**
+     * Tests if bookmarkExists() returns false when the given
+     * parameter is invalid.
+     *
+     * @return void
+     */
+    public function testBookmarkExistsInvalidParam()
+    {
+        $this->assertFalse($this->bs->bookmarkExists(false));
+        $this->assertFalse($this->bs->bookmarkExists(null));
+    }
+
+
+
+    /**
+     * Tests if bookmarkExists() returns true when a bookmark
+     * exists
+     *
+     * @return void
+     */
+    public function testBookmarkExistsTrue()
+    {
+        $bid = $this->addBookmark();
+        $bookmark = $this->bs->getBookmark($bid);
+
+        $this->assertTrue($this->bs->bookmarkExists($bookmark['bAddress']));
+    }
+
+
+
+    /**
+     * Tests if bookmarkExists() returns false when a bookmark
+     * does not exist
+     *
+     * @return void
+     */
+    public function testBookmarkExistsFalse()
+    {
+        $this->assertFalse($this->bs->bookmarkExists('does-not-exist'));
+    }
+
+
+
+    /**
+     * Tests if bookmarkExists() returns true when a bookmark
+     * exists for a user
+     *
+     * @return void
+     */
+    public function testBookmarkExistsUserTrue()
+    {
+        $bid = $this->addBookmark();
+        $bookmark = $this->bs->getBookmark($bid);
+
+        $this->assertTrue(
+            $this->bs->bookmarkExists(
+                $bookmark['bAddress'],
+                $bookmark['uId']
+            )
+        );
+    }
+
+
+
+    /**
+     * Tests if bookmarkExists() returns false when a bookmark
+     * does not exist for a user
+     *
+     * @return void
+     */
+    public function testBookmarkExistsUserFalse()
+    {
+        $this->assertFalse(
+            $this->bs->bookmarkExists('does-not-exist', 1234)
+        );
+    }
+
+
+
+    /**
+     * Tests if bookmarkExists() returns false when a bookmark
+     * does not exist for a user but for another user
+     *
+     * @return void
+     */
+    public function testBookmarkExistsOtherUser()
+    {
+        $bid = $this->addBookmark();
+        $bookmark = $this->bs->getBookmark($bid);
+
+        $this->assertFalse(
+            $this->bs->bookmarkExists(
+                $bookmark['bAddress'],
+                $bookmark['uId'] + 1
+            )
+        );
+    }
+
+
+
     /**
      * Test if countBookmarks() works with no bookmarks
      *