diff --git a/src/witness.c b/src/witness.c
index 23753f2..8efff56 100644
--- a/src/witness.c
+++ b/src/witness.c
@@ -3,12 +3,13 @@
 
 void
 witness_init(witness_t *witness, const char *name, witness_rank_t rank,
-    witness_comp_t *comp)
+    witness_comp_t *comp, void *opaque)
 {
 
 	witness->name = name;
 	witness->rank = rank;
 	witness->comp = comp;
+	witness->opaque = opaque;
 }
 
 #ifdef JEMALLOC_JET