diff --git a/Cargo.toml b/Cargo.toml
index 1df8b7e7..046a70af 100644
--- a/Cargo.toml
+++ b/Cargo.toml
@@ -7,6 +7,7 @@ authors = [
   "Phil Jenvey <pjenvey@underboss.org>",
 ]
 edition = "2018"
+rust = "1.39.0"
 
 [profile.release]
 # Enables line numbers in Sentry