diff --git a/Parsedown.php b/Parsedown.php
index 79f900b..91b28b4 100755
--- a/Parsedown.php
+++ b/Parsedown.php
@@ -81,7 +81,7 @@ class Parsedown
 		{
 			foreach ($matches as $matches)
 			{
-				$this->reference_map[$matches[1]] = $matches[2];
+				$this->reference_map[strtolower($matches[1])] = $matches[2];
 				
 				$text = str_replace($matches[0], '', $text);
 			}
@@ -526,14 +526,20 @@ class Parsedown
 		
 		# Reference(d) Link / Image 
 		
-		if ($this->reference_map and strpos($text, '[') !== FALSE and preg_match_all('/(!?)\[(.+?)\][ ]?\[(.+?)\]/', $text, $matches, PREG_SET_ORDER))
+		if ($this->reference_map and strpos($text, '[') !== FALSE and preg_match_all('/(!?)\[(.+?)\](?:[ ]?\[(.*?)\])?/ms', $text, $matches, PREG_SET_ORDER))
 		{
 			foreach ($matches as $matches)
 			{
-				if (array_key_exists($matches[3], $this->reference_map))
+				$link_difinition = isset($matches[3]) && $matches[3]
+					? $matches[3]
+					: $matches[2]; # implicit 
+				
+				$link_difinition = strtolower($link_difinition);
+				
+				if (isset($this->reference_map[$link_difinition]))
 				{
-					$url = $this->reference_map[$matches[3]];
-
+					$url = $this->reference_map[$link_difinition];
+					
 					if ($matches[1]) # image 
 					{
 						$element = '<img alt="'.$matches[2].'" src="'.$url.'">';
diff --git a/tests/data/reference_link.html b/tests/data/reference_link.html
index 84ed9e5..90a907b 100644
--- a/tests/data/reference_link.html
+++ b/tests/data/reference_link.html
@@ -1,8 +1,13 @@
-<p>Here's a <a href="http://parsedown.org">reference link</a>.</p>
-<p>Here's <a href="http://parsedown.org">one</a> with an alternative syntax.</p>
-<p>Here's <a href="http://parsedown.org">one</a> on the next line.</p>
-<p>Here's <a href="http://parsedown.org">one</a> on 2 lines.</p>
-<p>Here's <a href="http://parsedown.org/tests/">one</a> with a different URL.</p>
-<p>Here's <a href="http://parsedown.org">one</a> with a semantic name.</p>
-<p>Here's [one][404] with no definition.</p>
-<p>Here's an image: <img alt="Markdown Logo" src="https://raw.github.com/dcurtis/markdown-mark/master/png/32x20-solid.png"></p>
\ No newline at end of file
+<p>Here's a <a href="http://parsedown.org">reference link</a>.</p>
+<p>Here's <a href="http://parsedown.org">one</a> with an alternative syntax.</p>
+<p>Here's <a href="http://parsedown.org">one</a> on the next line.</p>
+<p>Here's <a href="http://parsedown.org">one</a> on 2 lines.</p>
+<p>Here's <a href="http://parsedown.org/tests/">one</a> with a different URL.</p>
+<p>Here's <a href="http://parsedown.org">one</a> with a semantic name.</p>
+<p>Here's [one][404] with no definition.</p>
+<p>Here's an image: <img alt="Markdown Logo" src="https://raw.github.com/dcurtis/markdown-mark/master/png/32x20-solid.png"></p>
+<p>Here's an <a href="http://google.com">implicit one</a>.</p>
+<p>Here's an <a href="http://google.com">implicit one</a>.</p>
+<p>Here's an <a href="http://google.com">implicit one</a> with an empty link definition.</p>
+<p>Here's a <a href="http://parsedown.org">multiline
+one</a> defined on 2 lines.</p>
\ No newline at end of file
diff --git a/tests/data/reference_link.md b/tests/data/reference_link.md
index e6fb2b3..9b2c620 100644
--- a/tests/data/reference_link.md
+++ b/tests/data/reference_link.md
@@ -1,29 +1,40 @@
-Here's a [reference link][1].
-
-[1]: http://parsedown.org
-
-Here's [one] [2] with an alternative syntax.
-
-[2] :http://parsedown.org
-
-Here's [one][3] on the next line.
-[3]: http://parsedown.org
-
-Here's [one][4] on 2 lines.
-
-[4]:
-http://parsedown.org
-
-Here's [one][5] with a different URL.
-
-[5]: http://parsedown.org/tests/
-
-Here's [one][the website] with a semantic name.
-
-[the website]: http://parsedown.org
-
-Here's [one][404] with no definition.
-
-Here's an image: ![Markdown Logo][image]
-
-[image]: https://raw.github.com/dcurtis/markdown-mark/master/png/32x20-solid.png
\ No newline at end of file
+Here's a [reference link][1].
+
+[1]: http://parsedown.org
+
+Here's [one] [2] with an alternative syntax.
+
+[2] :http://parsedown.org
+
+Here's [one][3] on the next line.
+[3]: http://parsedown.org
+
+Here's [one][4] on 2 lines.
+
+[4]:
+http://parsedown.org
+
+Here's [one][5] with a different URL.
+
+[5]: http://parsedown.org/tests/
+
+Here's [one][website] with a semantic name.
+
+[website]: http://parsedown.org
+
+Here's [one][404] with no definition.
+
+Here's an image: ![Markdown Logo][image]
+
+[image]: https://raw.github.com/dcurtis/markdown-mark/master/png/32x20-solid.png
+
+Here's an [implicit one].
+
+Here's an [implicit one].
+
+[implicit one]: http://google.com
+
+Here's an [implicit one][] with an empty link definition.
+
+Here's a [multiline
+one][website] defined on 2 lines.
\ No newline at end of file