diff --git a/perl/xs-src/unpack.c b/perl/xs-src/unpack.c
index fefb52e8..a4929c04 100644
--- a/perl/xs-src/unpack.c
+++ b/perl/xs-src/unpack.c
@@ -1,5 +1,6 @@
 #define NEED_newRV_noinc
 #define NEED_sv_2pv_flags
+#define NEED_my_snprintf
 #include "xshelper.h"
 
 #define MY_CXT_KEY "Data::MessagePack::_unpack_guts" XS_VERSION