diff --git a/lib/markdown2.py b/lib/markdown2.py
index 913559ba..91b6593c 100755
--- a/lib/markdown2.py
+++ b/lib/markdown2.py
@@ -1560,7 +1560,7 @@ def header_id_from_text(self,
 
         self._count_from_header_id[header_id] += 1
         if 0 == len(header_id) or self._count_from_header_id[header_id] > 1:
-            header_id += '-%s' % self._count_from_header_id[header_id]
+            header_id += ':%s' % self._count_from_header_id[header_id]
 
         return header_id
 
diff --git a/test/tm-cases/toc_duplicate_entries.html b/test/tm-cases/toc_duplicate_entries.html
index dc051bf7..e72e6e0b 100644
--- a/test/tm-cases/toc_duplicate_entries.html
+++ b/test/tm-cases/toc_duplicate_entries.html
@@ -1,5 +1,5 @@
 <h1 id="abc">abc</h1>
 
-<h1 id="abc-2">abc</h1>
+<h1 id="abc:2">abc</h1>
 
-<h1 id="abc-3">abc</h1>
+<h1 id="abc:3">abc</h1>
diff --git a/test/tm-cases/toc_duplicate_entries.toc_html b/test/tm-cases/toc_duplicate_entries.toc_html
index 72262013..a4861864 100644
--- a/test/tm-cases/toc_duplicate_entries.toc_html
+++ b/test/tm-cases/toc_duplicate_entries.toc_html
@@ -1,5 +1,5 @@
 <ul>
   <li><a href="#abc">abc</a></li>
-  <li><a href="#abc-2">abc</a></li>
-  <li><a href="#abc-3">abc</a></li>
+  <li><a href="#abc:2">abc</a></li>
+  <li><a href="#abc:3">abc</a></li>
 </ul>