1 files changed, 3 insertions, 2 deletions
diff --git a/synapse/rest/media/v1/thumbnail_resource.py b/synapse/rest/media/v1/thumbnail_resource.py
index a83535b97b..30421b663a 100644
--- a/synapse/rest/media/v1/thumbnail_resource.py
+++ b/synapse/rest/media/v1/thumbnail_resource.py
@@ -16,6 +16,7 @@
 
 import logging
 
+from synapse.api.errors import SynapseError
 from synapse.http.server import DirectServeJsonResource, set_cors_headers
 from synapse.http.servlet import parse_integer, parse_string
 
@@ -173,7 +174,7 @@ class ThumbnailResource(DirectServeJsonResource):
             await respond_with_file(request, desired_type, file_path)
         else:
             logger.warning("Failed to generate thumbnail")
-            respond_404(request)
+            raise SynapseError(400, "Failed to generate thumbnail.")
 
     async def _select_or_generate_remote_thumbnail(
         self,
@@ -235,7 +236,7 @@ class ThumbnailResource(DirectServeJsonResource):
             await respond_with_file(request, desired_type, file_path)
         else:
             logger.warning("Failed to generate thumbnail")
-            respond_404(request)
+            raise SynapseError(400, "Failed to generate thumbnail.")
 
     async def _respond_remote_thumbnail(
         self, request, server_name, media_id, width, height, method, m_type