diff --git a/Lib/ftplib.py b/Lib/ftplib.py
index aaf12fef6a2..ebc88df3b5a 100644
--- a/Lib/ftplib.py
+++ b/Lib/ftplib.py
@@ -392,7 +392,7 @@ class FTP:
         The callback function (2nd argument) is called for each line,
         with trailing CRLF stripped.  This creates a new port for you.
         print_line() is the default callback.'''
-        if not callback: callback = print_line
+        if not callable(callback): callback = print_line
         resp = self.sendcmd('TYPE A')
         conn = self.transfercmd(cmd)
         fp = conn.makefile('rb')
diff --git a/Misc/ACKS b/Misc/ACKS
index b4135402dfa..1897e307da9 100644
--- a/Misc/ACKS
+++ b/Misc/ACKS
@@ -226,6 +226,7 @@ John Interrante
 Ben Jackson
 Paul Jackson
 David Jacobs
+Geert Jansen
 Jack Jansen
 Bill Janssen
 Drew Jenkins