No previous prototype for function

I use two versions of Monetdb. 1 is PythonUDF and another Monetdb 11.21.13. Function "bitand" is compiled and used well in Monetdb, but when I try to compile PythonUDF it gives me errors:

udf.c:14:1: error: no previous prototype for 'UDFbitand' [-Werror=missing-prototypes] UDFbitand(flt *ret, lng*a, lng *b) ^ cc1: all warnings being treated as errors Makefile:876: recipe for target 'lib_udf_la-udf.lo' failed

any ideas? thanks in advance.