diff --git a/Lib/smtpd.py b/Lib/smtpd.py
index 599e79b..32f45ae 100755
--- a/Lib/smtpd.py
+++ b/Lib/smtpd.py
@@ -275,7 +275,7 @@
             return
         elif limit:
             self.num_bytes += len(data)
-        self.received_lines.append(str(data, "utf8"))
+        self.received_lines.append(str(data, "utf-8"))
 
     # Implementation of base class abstract method
     def found_terminator(self):