diff --git a/go.mod b/go.mod
index 46c9aab..58b7d0d 100644
--- a/go.mod
+++ b/go.mod
@@ -15,3 +15,5 @@
 module github.com/google/btree
 
 go 1.18
+
+require github.com/petar/GoLLRB v0.0.0-20210522233825-ae3b015fd3e9 // indirect