diff --git a/boards/forms.py b/boards/forms.py
--- a/boards/forms.py
+++ b/boards/forms.py
@@ -38,7 +38,7 @@ class PostForm(forms.Form):
 
 
 class ThreadForm(PostForm):
-    INVALID_TAG_CHARACTERS = ['+', '/', '&', '=', '?']
+    INVALID_TAG_CHARACTERS = ['+', '/', '&', '=', '?', '-']
 
     tags = forms.CharField(max_length=100)