diff --git a/apps/converter/backends/python/base.py b/apps/converter/backends/python/base.py
index 910a143437..708124fb07 100644
--- a/apps/converter/backends/python/base.py
+++ b/apps/converter/backends/python/base.py
@@ -38,7 +38,7 @@ class ConverterClass(ConverterBase):
         try:
             im = Image.open(input_filepath)
         except IOError:  #cannot identify image file
-            return UnknownFileFormat
+            raise UnknownFileFormat
             
         try:
             while 1: