diff --git a/docker/Start-Codeman.sh b/docker/Start-Codeman.sh
index 0b2806ce..d30737cb 100644
--- a/docker/Start-Codeman.sh
+++ b/docker/Start-Codeman.sh
@@ -209,8 +209,9 @@ generate_password() {
 
 # Compose reads .env values with its own dotenv rules: `$` interpolates and an
 # unquoted ` #` starts a comment. A single-quoted value is taken literally, so
-# anything beyond plain path characters is written that way (the accept_*
-# checks below refuse the one character it cannot hold, a single quote).
+# anything beyond plain path characters is written that way. It cannot hold a
+# single quote, and a backslash just before the closing quote escapes that quote,
+# so the whole file fails to parse: the accept_* checks below refuse both.
 env_quote() {
   local re='^[A-Za-z0-9._/@:+-]*$'
   if [[ "$1" =~ $re ]]; then
@@ -237,6 +238,10 @@ accept_appdata_path() {
       printf '  The path cannot contain a single quote or a line break.\n' >&2
       return 1
       ;;
+    *\\)
+      printf '  The path cannot end in a backslash.\n' >&2
+      return 1
+      ;;
   esac
   if [[ "$p" != /* ]]; then
     printf '  Use an absolute path, one that starts with /.\n' >&2
@@ -277,6 +282,10 @@ accept_password() {
       printf '  The password cannot contain a single quote or a line break.\n' >&2
       return 1
       ;;
+    *\\)
+      printf '  The password cannot end in a backslash.\n' >&2
+      return 1
+      ;;
   esac
   if ((${#1} < 8)); then
     printf '  Use at least 8 characters.\n' >&2
diff --git a/test/docker-start-setup.test.ts b/test/docker-start-setup.test.ts
index bc71b740..05e13824 100644
--- a/test/docker-start-setup.test.ts
+++ b/test/docker-start-setup.test.ts
@@ -228,6 +228,21 @@ function envValue(text: string, key: string): string | undefined {
   return raw.startsWith("'") && raw.endsWith("'") ? raw.slice(1, -1) : raw;
 }
 
+/**
+ * What Compose reads from a single-quoted dotenv value, or null when it refuses
+ * the file with `unterminated quoted value`. A backslash there escapes the next
+ * character, so `'longpass\\'` never closes, while bash (and so the stub) ends
+ * the same value at that quote. Measured on Compose 2.33.0 and 5.5.0.
+ */
+function composeReads(quoted: string): string | null {
+  let escaped = false;
+  for (let i = 1; i < quoted.length; i++) {
+    if (quoted[i] === "'" && !escaped) return i === quoted.length - 1 ? quoted.slice(1, i) : null;
+    escaped = quoted[i] === '\\' && !escaped;
+  }
+  return null;
+}
+
 describe('Start-Codeman.sh first run (no docker/.env yet)', () => {
   it('parses under bash -n', () => {
     execFileSync('bash', ['-n', join(ROOT, 'docker/Start-Codeman.sh')]);
@@ -316,12 +331,32 @@ describe('Start-Codeman.sh first run (no docker/.env yet)', () => {
     ['a single quote', "it's-a-password"],
     ['the example placeholder', 'changeme'],
     ['fewer than 8 characters', 'short'],
+    ['a trailing backslash, which would escape the closing quote', 'longpass\\'],
   ])('refuses a preset password with %s', (_name, password) => {
     const r = runStart(['--setup-only'], { env: { CODEMAN_PASSWORD: password } });
     expect(r.status).toBe(1);
     expect(r.env).toBeNull();
   });
 
+  it('refuses a data folder ending in a backslash, even behind a trailing slash', () => {
+    for (const path of ['/srv/data\\', '/srv/data\\/']) {
+      const r = runStart(['--setup-only'], { env: { CODEMAN_APPDATA_PATH: path } });
+      expect(r.status).toBe(1);
+      expect(r.stderr).toMatch(/cannot end in a backslash/);
+      expect(r.env).toBeNull();
+    }
+  });
+
+  it.each(['mid\\dle-pass', 'pa$$ #word', 'back`tick"quote', 'tab\there'])(
+    'writes %j so Compose reads it back exactly',
+    (password) => {
+      const r = runStart(['--setup-only'], { env: { CODEMAN_PASSWORD: password } });
+      expect(r.status, r.stderr).toBe(0);
+      const line = (r.env as string).split('\n').find((l) => l.startsWith('CODEMAN_PASSWORD=')) as string;
+      expect(composeReads(line.slice('CODEMAN_PASSWORD='.length))).toBe(password);
+    }
+  );
+
   it('never rewrites an existing docker/.env', () => {
     const existing = '# hand-written\nCODEMAN_PASSWORD=mine-and-only-mine\nCODEMAN_APPDATA_PATH=/x\n';
     const r = runStart(['--setup-only'], { existingEnv: existing });