diff --git a/src/uu/tee/Cargo.toml b/src/uu/tee/Cargo.toml
index 1c263c596..a984a2f66 100644
--- a/src/uu/tee/Cargo.toml
+++ b/src/uu/tee/Cargo.toml
@@ -17,7 +17,7 @@ path = "src/tee.rs"
 [dependencies]
 clap = { version = "2.33", features = ["wrap_help"] }
 libc = "0.2.42"
-retain_mut = "0.1.2"
+retain_mut = "=0.1.2" # ToDO: [2021-01-01; rivy; maint/MinSRV] ~ v0.1.5 uses const generics which aren't stabilized until rust v1.51.0
 uucore = { version=">=0.0.10", package="uucore", path="../../uucore", features=["libc"] }
 uucore_procs = { version=">=0.0.7", package="uucore_procs", path="../../uucore_procs" }