diff --git a/.env.example b/.env.example
index af3af2c..73dedd0 100644
--- a/.env.example
+++ b/.env.example
@@ -15,13 +15,16 @@ PYMC_REPEATER_IMAGE=pymcdev/pymc-repeater:main
 # PYMC_CONFIG_VOLUME=/opt/pymc-repeater/config
 # PYMC_DATA_VOLUME=/opt/pymc-repeater/data
 
-# SPI/GPIO access uses the host's numeric group IDs. Check your host with:
+# Serial/SPI/GPIO access uses the host's numeric group IDs. Check your host with:
+#   getent group dialout
 #   getent group gpio
 #   getent group spi
 # Example output:
+#   dialout:x:20:
 #   gpio:x:997:
 #   spi:x:999:
 # Put the third field from each output line below.
+DIALOUT_GID=20
 GPIO_GID=986
 SPI_GID=989
 
diff --git a/README.md b/README.md
index be44d1a..c16e43c 100644
--- a/README.md
+++ b/README.md
@@ -400,8 +400,8 @@ Copy `.env.example` to `.env` before starting:
 cp .env.example .env
 ```
 
-Set `GPIO_GID` and `SPI_GID` from `getent group gpio` and `getent group spi`
-if your host values are different.
+Set `DIALOUT_GID`, `GPIO_GID`, and `SPI_GID` from `getent group dialout`,
+`getent group gpio`, and `getent group spi` if your host values are different.
 
 Default storage should use Docker named volumes. This avoids Portainer creating
 root-owned `./config` and `./data` bind mount folders on first start. If you
@@ -414,8 +414,8 @@ that source as a directory, which breaks startup.
 ### Setup
 
 1. Copy `.env.example` to `.env`.
-2. Review `.env` and update `PYMC_REPEATER_IMAGE`, `GPIO_GID`, or `SPI_GID`
-   if needed.
+2. Review `.env` and update `PYMC_REPEATER_IMAGE`, `DIALOUT_GID`,
+   `GPIO_GID`, or `SPI_GID` if needed.
 3. Configure `docker-compose.yml` for your hardware and device paths.
 4. Uncomment the USB device mapping only if your host has that device path.
 5. Pull and start the container.
@@ -447,6 +447,7 @@ services:
       - SYS_RAWIO
 
     group_add:
+      - "${DIALOUT_GID:-20}"
       - "${GPIO_GID:-986}"
       - "${SPI_GID:-989}"
       - plugdev
diff --git a/docker-compose.build.yml b/docker-compose.build.yml
index 0f1c2f6..bfcc204 100644
--- a/docker-compose.build.yml
+++ b/docker-compose.build.yml
@@ -7,5 +7,6 @@ services:
       args:
         PUID: ${PUID:-15888}
         PGID: ${PGID:-15888}
+        DIALOUT_GID: ${DIALOUT_GID:-20}
         GPIO_GID: ${GPIO_GID:-986}
         SPI_GID: ${SPI_GID:-989}
diff --git a/docker-compose.yml b/docker-compose.yml
index d2aff30..31301f6 100644
--- a/docker-compose.yml
+++ b/docker-compose.yml
@@ -16,6 +16,7 @@ services:
       - SYS_RAWIO
     # USB DEVICE PERMISSIONS
     group_add:
+      - "${DIALOUT_GID:-20}"
       - "${GPIO_GID:-986}"
       - "${SPI_GID:-989}"
       - plugdev
diff --git a/dockerfile b/dockerfile
index 39e2f6d..17e06c3 100644
--- a/dockerfile
+++ b/dockerfile
@@ -5,6 +5,7 @@ ARG USER=repeater
 ARG GROUP=repeater
 ARG PUID=15888
 ARG PGID=15888
+ARG DIALOUT_GID=20
 ARG GPIO_GID=986
 ARG SPI_GID=989
 ARG TARGETARCH
@@ -19,6 +20,7 @@ ENV INSTALL_DIR=/opt/pymc_repeater \
     SETUPTOOLS_SCM_PRETEND_VERSION_FOR_PYMC_REPEATER=${PACKAGE_VERSION} \
     PUID=${PUID} \
     PGID=${PGID} \
+    DIALOUT_GID=${DIALOUT_GID} \
     GPIO_GID=${GPIO_GID} \
     SPI_GID=${SPI_GID}
 
@@ -49,10 +51,11 @@ RUN arch="${TARGETARCH:-}" \
 
 # Create the group and user in order to run without root privileges
 RUN groupadd --gid "$PGID" "$GROUP" \
+    && (getent group dialout >/dev/null || groupadd --gid "$DIALOUT_GID" dialout) \
     && groupadd --gid "$GPIO_GID" gpio \
     && groupadd --gid "$SPI_GID" spi \
     && useradd --uid "$PUID" --gid "$PGID" --home-dir "$HOME_DIR" --create-home --shell /usr/bin/bash "$USER" \
-    && usermod -a -G gpio,spi "$USER"
+    && usermod -a -G dialout,gpio,spi "$USER"
 
 # Create runtime directories
 RUN mkdir -p ${INSTALL_DIR} ${CONFIG_DIR} ${DATA_DIR} \