diff --git a/boards/models/post/sync.py b/boards/models/post/sync.py
--- a/boards/models/post/sync.py
+++ b/boards/models/post/sync.py
@@ -16,6 +16,7 @@ EXCEPTION_DOWNLOAD = 'File was not downl
 EXCEPTION_HASH = 'File hash does not match attachment hash.'
 EXCEPTION_SIGNATURE = 'Invalid model signature for {}.'
 EXCEPTION_AUTHOR_SIGNATURE = 'Model {} has no author signature.'
+EXCEPTION_THREAD = 'No thread exists for post {}'
 ENCODING_UNICODE = 'unicode'
 
 TAG_MODEL = 'model'
@@ -217,7 +218,7 @@ class SyncManager:
                 if exists:
                     opening_post = Post.objects.get(global_id=op_global_id)
                 else:
-                    logger.debug('No thread exists for post {}'.format(global_id))
+                    raise Exception(EXCEPTION_THREAD.format(global_id))
             else:
                 opening_post = None
                 tag_tags = tag_content.find(TAG_TAGS)
@@ -375,4 +376,4 @@ class SyncManager:
         if opening_post:
             ThreadFilter().add_filter(model, opening_post)
 
-        return et.tostring(request, 'unicode')
\ No newline at end of file
+        return et.tostring(request, 'unicode')