diff --git a/code-server/.env.example b/code-server/.env.example
index 87e38c4..27f8390 100644
--- a/code-server/.env.example
+++ b/code-server/.env.example
@@ -10,6 +10,6 @@ PASSWORD=
 GIT_NAME=
 GIT_EMAIL=
 
-# Container hostname, shown in the shell prompt.
+# Container hostname, also passed in as HOST -- the name zsh's prompt shows.
 # Not named HOSTNAME: the deploying shell's own HOSTNAME would override it.
 SERVICE_HOSTNAME=code-server
diff --git a/code-server/README.md b/code-server/README.md
index bc50818..1c1e0e6 100644
--- a/code-server/README.md
+++ b/code-server/README.md
@@ -98,7 +98,7 @@ new binary overwrites the old one.
 | --- | --- |
 | `PASSWORD` | Web UI login. Required. |
 | `GIT_NAME` / `GIT_EMAIL` | Git author and committer identity |
-| `SERVICE_HOSTNAME` | Container hostname, and the name the shell prompt shows |
+| `SERVICE_HOSTNAME` | Container hostname, and the name the shell prompt shows (also passed as `HOST`) |
 
 Generate a password with `openssl rand -base64 24`.
 
@@ -109,6 +109,13 @@ can only read from inside the container.
 The `coder` user has passwordless `sudo`, as the image sets it up. Anyone who
 can log in to the editor is root in the container.
 
+`SERVICE_HOSTNAME` is used twice: as the container's `hostname:` and as the
+`HOST` variable inside it. Coolify injects `HOST=0.0.0.0` into every compose
+app, and zsh seeds `$HOST` and the `%m`/`%M` prompt escapes from that variable
+rather than calling `gethostname()`, so a zsh prompt reads `0`. code-server
+itself never reads `HOST`; it binds through `--bind-addr`. bash is unaffected;
+its `\h` uses the real hostname.
+
 ## Docker access
 
 The host's Docker socket is bind-mounted at `/var/run/docker.sock`. The image
diff --git a/code-server/compose.yml b/code-server/compose.yml
index 62ccbe1..cc44bf3 100644
--- a/code-server/compose.yml
+++ b/code-server/compose.yml
@@ -11,6 +11,7 @@ services:
       - GIT_AUTHOR_EMAIL=${GIT_EMAIL}
       - GIT_COMMITTER_NAME=${GIT_NAME}
       - GIT_COMMITTER_EMAIL=${GIT_EMAIL}
+      - HOST=${SERVICE_HOSTNAME}
     volumes:
       - 'code-server-home:/home/coder'
       - 'code-server-workspace:/workspace'