diff --git a/cps/__init__.py b/cps/__init__.py
index fead0d2f43..642f6a6e16 100755
--- a/cps/__init__.py
+++ b/cps/__init__.py
@@ -70,8 +70,8 @@
 mimetypes.add_type('image/vnd.djv', '.djvu')
 mimetypes.add_type('application/mpeg', '.mpeg')
 mimetypes.add_type('audio/mpeg', '.mp3')
-mimetypes.add_type('application/mp4', '.m4a')
-mimetypes.add_type('application/mp4', '.m4b')
+mimetypes.add_type('audio/x-m4a', '.m4a')
+mimetypes.add_type('audio/x-m4a', '.m4b')
 mimetypes.add_type('audio/ogg', '.ogg')
 mimetypes.add_type('application/ogg', '.oga')
 mimetypes.add_type('text/css', '.css')
diff --git a/cps/file_helper.py b/cps/file_helper.py
index 095b5ee096..d618231100 100644
--- a/cps/file_helper.py
+++ b/cps/file_helper.py
@@ -47,11 +47,11 @@ def del_temp_dir():
 
 def validate_mime_type(file_buffer, allowed_extensions):
     mime = magic.Magic(mime=True)
-    allowed_mimetypes =list()
+    allowed_mimetypes = list()
     for x in allowed_extensions:
         try:
             allowed_mimetypes.append(mimetypes.types_map["." + x])
-        except KeyError as e:
+        except KeyError:
             log.error("Unkown mimetype for Extension: {}".format(x))
     tmp_mime_type = mime.from_buffer(file_buffer.read())
     file_buffer.seek(0)
@@ -66,6 +66,5 @@ def validate_mime_type(file_buffer, allowed_extensions):
                     return True
         except:
             file_buffer.seek(0)
-            pass
-    
+    log.error("Mimetype '{}' not found in allowed types".format(tmp_mime_type))
     return False
diff --git a/optional-requirements.txt b/optional-requirements.txt
index 77f41e1e25..3f6b6e37d6 100644
--- a/optional-requirements.txt
+++ b/optional-requirements.txt
@@ -42,7 +42,7 @@ natsort>=2.2.0,<8.5.0
 comicapi>=2.2.0,<3.3.0
 
 # Kobo integration
-jsonschema>=3.2.0,<4.23.0
+jsonschema>=3.2.0,<4.24.0
 
 # Hide console Window on Windows
 pywin32>=220,<310 ; sys_platform == 'win32'