--- a/src/vmod_digest.vcc
+++ b/src/vmod_digest.vcc
@@ -1,4 +1,5 @@
 $Module digest 3 Varnish Digest Module
+$ABI vrt
 $Event event_function
 $Function STRING hmac_sha256(STRING, STRING)
 $Function STRING hmac_sha1(STRING, STRING)
