diff --git a/git-compat-util.h b/git-compat-util.h
index f649e81..348b9dc 100644
--- a/git-compat-util.h
+++ b/git-compat-util.h
@@ -744,6 +744,9 @@
 	return (size_t)len;
 }
 
+__attribute__((format (printf, 3, 4)))
+extern int xsnprintf(char *dst, size_t max, const char *fmt, ...);
+
 /* in ctype.c, for kwset users */
 extern const unsigned char tolower_trans_tbl[256];