diff --git a/markdown-mode.el b/markdown-mode.el
index ecc82f77..966d650b 100644
--- a/markdown-mode.el
+++ b/markdown-mode.el
@@ -1302,7 +1302,7 @@ Group 2 matches only the label, without the surrounding markup.
 Group 3 matches the closing square bracket.")
 
 (defconst markdown-regex-header
-  "^\\(?:\\(.+\\)\n\\(=+\\)\\|\\(.+\\)\n\\(-+\\)\\|\\(#+\\)\\s-*\\(.*?\\)\\s-*?\\(#*\\)\\)$"
+  "^\\(?:\\(.+\\)\n\\(=+\\)\\|\\(.+\\)\n\\(-+\\)\\|\\(#+\\)\\s-+\\(.*?\\)\\s-*?\\(#*\\)\\)$"
   "Regexp identifying Markdown headers.")
 
 (defconst markdown-regex-header-1-atx