diff --git a/libguile/whippet/src/root-worklist.h b/libguile/whippet/src/root-worklist.h
index 45ede8595..b58d5b549 100644
--- a/libguile/whippet/src/root-worklist.h
+++ b/libguile/whippet/src/root-worklist.h
@@ -22,7 +22,7 @@ struct root_worklist {
   struct gc_root *buf;
 };
 
-void
+static void
 root_worklist_alloc(struct root_worklist *q) {
   q->buf = realloc(q->buf, q->size * sizeof(struct gc_root));
   if (!q->buf) {