diff --git a/Dockerfile b/Dockerfile
index cddad4a..5e63f32 100644
--- a/Dockerfile
+++ b/Dockerfile
@@ -1,5 +1,5 @@
 FROM ubuntu:18.04
-ARG RUST_TOOLCHAIN="1.35.0"
+ARG RUST_TOOLCHAIN="1.39.0"
 
 # Adding rust binaries to PATH.
 ENV PATH="$PATH:/root/.cargo/bin"
diff --git a/README.md b/README.md
index 7fa7a5c..a0c6392 100644
--- a/README.md
+++ b/README.md
@@ -63,12 +63,15 @@ Rust targets on aarch64:
 
 ### Publishing a New Version
 
+In this example, we assume the current version is `v3` and we want to publish
+a newer `v4` container version.
+
 On an aarch64 platform:
 
 ```bash
 > cd rust-vmm-dev-container
 > # Build a container image for aarch64
-> docker build -t rustvmm/dev:aarch64 -f Dockerfile .
+> docker build -t rustvmm/dev:v4_aarch64 -f Dockerfile .
 > docker images
 REPOSITORY             TAG                 IMAGE ID            CREATED             SIZE
 rustvmm/dev            aarch64             f3fd02dfb213        21 hours ago        1.13GB