diff --git a/imap_filter/imap_filter.py b/imap_filter/imap_filter.py
index c123663..b25f84b 100644
--- a/imap_filter/imap_filter.py
+++ b/imap_filter/imap_filter.py
@@ -132,7 +132,10 @@ class ImapFilter:
                 data
             )
             return {"match": False}
-        part = data[1].decode('utf-8')
+        try:
+            part = data[1].decode('utf-8')
+        except UnicodeDecodeError:
+            part = data[1]
         message = email.message_from_string(part)
         decoded_field = email.header.decode_header(message.get(mfilter['field'], ""))
         if isinstance(decoded_field[0][0], str):