The warning was:
m_simple.c: In function ‘parse_simple’:
m_simple.c:142:4: warning: format ‘%ld’ expects argument of type ‘long int’, but argument 3 has type ‘size_t’ [-Wformat]

Useful to be able to compile with -Werror.
Signed-off-by: Nicolas Dichtel <nicolas.dichtel@6wind.com>