diff --git a/pyproject.toml b/pyproject.toml
index 6e40c87..195be69 100644
--- a/pyproject.toml
+++ b/pyproject.toml
@@ -16,6 +16,7 @@ keywords = ["hypercore", "hypercore-protocol"]
 [tool.poetry.dependencies]
 python = "^3.6"
 attrs = "^19.3.0"
+pyvarint = "^0.0.1-alpha.2"
 
 [tool.poetry.dev-dependencies]
 black = "^19.10b0"