diff --git a/4_post_to_wiki.py b/4_post_to_wiki.py
index e7bd30a..34fccba 100644
--- a/4_post_to_wiki.py
+++ b/4_post_to_wiki.py
@@ -28,6 +28,8 @@ def post(files):
                 files.append(filepath)
 
     for filepath in files:
+        if OUTDIR_MEDIAWIKI not in filepath:
+            raise ValueError("{filepath} not in {OUTDIR_MEDIAWIKI}")
         filename = os.path.basename(filepath)
 
         article_name = WIKI_ARTICLE_PREFIX + filename.replace(".mediawiki", "")