diff --git a/src/calibre/utils/terminal.py b/src/calibre/utils/terminal.py
index b20c05f8ac..0736ba87d8 100644
--- a/src/calibre/utils/terminal.py
+++ b/src/calibre/utils/terminal.py
@@ -146,7 +146,7 @@ class ANSIStream(Detect):
 
     def __init__(self, stream=None):
         super(ANSIStream, self).__init__(stream)
-        self.encoding = getattr(self.stream, 'encoding', 'utf-8')
+        self.encoding = getattr(self.stream, 'encoding', 'utf-8') or 'utf-8'
 
     def write(self, text):
         if isinstance(text, type(u'')):