diff --git a/docker_images/mbed-os-env/Dockerfile b/docker_images/mbed-os-env/Dockerfile
index 8e6c08f2f2..942a2b72ce 100644
--- a/docker_images/mbed-os-env/Dockerfile
+++ b/docker_images/mbed-os-env/Dockerfile
@@ -2,6 +2,11 @@
 # Pull base image
 FROM ubuntu:20.04
 
+# ------------------------------------------------------------------------------
+# set locale
+ENV LANG C.UTF-8
+ENV LC_ALL C.UTF-8
+
 # ------------------------------------------------------------------------------
 # Arguments
 ARG WORKDIR=/root