diff --git a/pelican/readers.py b/pelican/readers.py
index 38632222..f18826a9 100644
--- a/pelican/readers.py
+++ b/pelican/readers.py
@@ -49,7 +49,11 @@ class MarkdownReader(object):
         
         metadatas = {}
         for name, value in md.Meta.items():
-            metadatas[name.lower()] = value[0] 
+            if name in _METADATAS_FIELDS:
+                meta = _METADATAS_FIELDS[name](value[0])
+            else:
+                meta = value[0]
+            metadatas[name.lower()] = meta
         return content, metadatas
 
 _EXTENSIONS = {'rst': RstReader, 'md': MarkdownReader}  # supported formats