diff --git a/pytest_doctestplus/plugin.py b/pytest_doctestplus/plugin.py
index ee26a58..319c177 100644
--- a/pytest_doctestplus/plugin.py
+++ b/pytest_doctestplus/plugin.py
@@ -30,7 +30,8 @@
 comment_characters = {
     '.txt': '#',
     '.tex': '%',
-    '.rst': r'\.\.'
+    '.rst': r'\.\.',
+    '.md': '<!--'
 }