diff --git a/package/rsync/rsync.mk b/package/rsync/rsync.mk
index 81ad4b9291..7ff7ca6eef 100644
--- a/package/rsync/rsync.mk
+++ b/package/rsync/rsync.mk
@@ -11,6 +11,9 @@ RSYNC_LICENSE_FILES = COPYING
 RSYNC_CPE_ID_VENDOR = samba
 RSYNC_SELINUX_MODULES = rsync
 RSYNC_DEPENDENCIES = zlib popt
+# We know that our C library is modern enough for C99 vsnprintf(). Since
+# configure can't detect this, we tell configure that vsnprintf() is safe.
+RSYNC_CONF_ENV = rsync_cv_HAVE_C99_VSNPRINTF=yes
 RSYNC_CONF_OPTS = \
 	--with-included-zlib=no \
 	--with-included-popt=no \