global SyntaxError different in Python REPL vs Bpython

Consider the following code (which rightly generates a SyntaxError):

>>> counter = 0
>>> def increment():
...     counter += 1
...     global counter

In the Python REPL, this generates the following error:

SyntaxError: name 'counter' is assigned to before global declaration

However, in Bpython, the following error occurs:

SyntaxError: incomplete input

The Bpython error appears to be incorrect to me?