diff --git a/keymaps/markdown-preview.cson b/keymaps/markdown-preview.cson
index a5c3b7a..4235566 100644
--- a/keymaps/markdown-preview.cson
+++ b/keymaps/markdown-preview.cson
@@ -1,4 +1,4 @@
-'atom-workspace, atom-workspace atom-text-editor':
+'atom-text-editor[data-grammar="source gfm"]':
   'ctrl-M': 'markdown-preview:toggle'
 
 '.platform-darwin .markdown-preview':