diff --git a/docker-cmd-mac.sh b/docker-cmd-mac.sh
index b4815a5..9c2087a 100755
--- a/docker-cmd-mac.sh
+++ b/docker-cmd-mac.sh
@@ -23,6 +23,8 @@ EXEC=false
 CONTAINER=""
 DEVEL_DIR=""
 LEARN_DIR=""
+USER_ID=""
+GROUP_ID=""
 COMMAND=""
 EXP=""
 DETACH=false
@@ -40,6 +42,8 @@ function print_help {
     echo "  DETACH: ($DETACH) [--detach]"
     echo "  DEVELOPMENT dir \"$DEVEL_DIR\" [-d, --devel]"
     echo "  LEARNING dir \"$LEARN_DIR\" [-l, --learn]"
+    echo "  USER ID \"$USER_ID\" [-u, --uid]"
+    echo "  GROUP ID \"$GROUP_ID\" [-g, --gid]"
 }
 
 for arg in "$@"
@@ -86,6 +90,12 @@ do
         -l=*|--learn=*)
         LEARN_DIR="${arg#*=}"
         ;;
+        -u=*|--uid=*)
+        USER_ID="${arg#*=}"
+        ;;
+        -g=*|--gid=*)
+        GROUP_ID="${arg#*=}"
+        ;;
         *)
         # unknown option
         echo "Unknown option \"$arg\""
@@ -105,14 +115,14 @@ if [[ "$BUILD" = true ]]; then
     if [[ "$CACHE" = true ]]; then
         echo "Building the docker container using the cache, if present."
         docker build \
-            --build-arg USER_ID=$(id -u ${USER}) \
-            --build-arg GROUP_ID=$(id -g ${USER}) \
+            --build-arg USER_ID="$USER_ID" \
+            --build-arg GROUP_ID="$GROUP_ID" \
             -t "$IMAGE_NAME" "$IMAGE_FOLDER"
     else
         echo "Building the docker container ignoring the cache, even if present."
         docker build \
-            --build-arg USER_ID=$(id -u ${USER}) \
-            --build-arg GROUP_ID=$(id -g ${USER}) \
+            --build-arg USER_ID="$USER_ID" \
+            --build-arg GROUP_ID="$GROUP_ID" \
             --no-cache -t "$IMAGE_NAME" "$IMAGE_FOLDER"
     fi
 fi
diff --git a/docker-image-mac/Dockerfile b/docker-image-mac/Dockerfile
index 4e3e2d5..3e9d83a 100644
--- a/docker-image-mac/Dockerfile
+++ b/docker-image-mac/Dockerfile
@@ -69,8 +69,8 @@ RUN python -m pip install ray[rllib]
 RUN python -m pip install ray[tune]
 
 # Working user
-RUN groupadd --gid 222 alice && \
-    useradd -m -s /bin/bash -u 502 -g 222 alice && \
+RUN groupadd --gid ${GROUP_ID} alice && \
+    useradd -m -s /bin/bash -u ${USER_ID} -g ${GROUP_ID} alice && \
     echo "alice:alice" | chpasswd && adduser alice sudo
 USER alice
 
diff --git a/docs/howto-mac.md b/docs/howto-mac.md
index 1d5188e..99be8ac 100644
--- a/docs/howto-mac.md
+++ b/docs/howto-mac.md
@@ -4,11 +4,12 @@
 
 Basic command to use:
 
-`bash docker-cmd-mac.sh --build`
+`bash docker-cmd-mac.sh --build --uid=502 --gid=222`
 
 - The default tag name of this image is `tf-gpu-sumo-{today_date}`. You can also add option such as `--image-name={new_name}` to specify your own name;
 - The default path of the dockerfile to be used is `docker-image-mac`. You can adapt to your setting by using option `--image-folder`;
 - The default image building process does not use cache. You can enable it by adding the option `--cache`.
+- The user id and group id are suggested as 502 and 222 respectively. The range of valid values on MacOS needs to be further studied.
 
 ## Step 2: Run a container of the built image
 
@@ -46,6 +47,8 @@ Default parameters:
   DETACH: (true)                        [--detach]
   DEVELOPMENT dir ""                    [-d, --devel]
   LEARNING dir ""                       [-l, --learn]
+  USER_ID ""                            [-u, --uid]
+  GROUP_ID ""                           [-g, --gid]
 ```
 
 Example of use: