diff --git a/Dockerfile b/Dockerfile
index 8c9fd0b44..807f18ec9 100644
--- a/Dockerfile
+++ b/Dockerfile
@@ -116,6 +116,7 @@ WORKDIR ${CML_RUNNER_PATH}
 # SET SPECIFIC ENVIRONMENT VARIABLES
 ENV IN_DOCKER=1
 ENV RUNNER_ALLOW_RUNASROOT=1
+# Environment variable used by cml to detect it's been installed using the docker image.
 ENV _CML_CONTAINER_IMAGE=true
 
 # DEFINE ENTRY POINT AND COMMAND