diff --git a/loris/resolver.py b/loris/resolver.py
index 9c5c838f..522a6e81 100644
--- a/loris/resolver.py
+++ b/loris/resolver.py
@@ -298,7 +298,8 @@ def cached_file_for_ident(self, ident):
     def cache_file_extension(self, ident, response):
         if 'content-type' in response.headers:
             try:
-                extension = self.get_format(ident, constants.FORMATS_BY_MEDIA_TYPE[response.headers['content-type']])
+                content_type = response.headers['content-type'].split(';')[0]
+                extension = self.get_format(ident, constants.FORMATS_BY_MEDIA_TYPE[content_type])
             except KeyError:
                 logger.warn('Your server may be responding with incorrect content-types. Reported %s for ident %s.',
                             response.headers['content-type'], ident)