diff --git a/src/command-options/build-options.ts b/src/command-options/build-options.ts
index 7dd74f8..f194e95 100644
--- a/src/command-options/build-options.ts
+++ b/src/command-options/build-options.ts
@@ -144,6 +144,15 @@ export class BuildOptions implements IOptions {
         demandOption: false,
         default: defaultDockerMemoryLimit(),
       })
+      .option('dockerShmSize', {
+        description: String.dedent`Size of /dev/shm to assign the docker container, using the format <number><unit>
+        (m or g). Unity 6.6 beta / 6.7 alpha editors have been reported to fail with "Insufficient shared memory
+        available" against Docker's 64m default (see game-ci/unity-test-runner#307); leave unset to use Docker's
+        own default on older/stable editors that don't need it.`,
+        type: 'string',
+        demandOption: false,
+        default: '',
+      })
       .option('dockerIsolationMode', {
         description: String.dedent`Windows only. Isolation mode to use for the docker container. Can be one of
         process, hyperv, or default. Default will pick the default mode as described by Microsoft where server
diff --git a/src/model/docker.test.ts b/src/model/docker.test.ts
index 39eead0..d5fe93f 100644
--- a/src/model/docker.test.ts
+++ b/src/model/docker.test.ts
@@ -81,14 +81,31 @@ describe('Docker', () => {
       engine: 'unity',
       dockerCpuLimit: '4',
       dockerMemoryLimit: '8192m',
+      dockerShmSize: '1024m',
       useHostNetwork: true,
     });
 
     expect(command).toContain('--cpus=4');
     expect(command).toContain('--memory=8192m');
+    expect(command).toContain('--shm-size=1024m');
     expect(command).toContain('--net=host');
   });
 
+  it('omits --shm-size when dockerShmSize is not set (game-ci/unity-test-runner#307)', () => {
+    const command = (Docker as any).getLinuxCommand('game-ci/unity-editor-stub:latest', {
+      hostOS: 'linux',
+      currentWorkDir: '/home/runner/work/cli/cli',
+      homeDir: '/home/runner',
+      cliDistPath: '/home/runner/work/cli/cli/dist',
+      sshAgent: '',
+      gitPrivateToken: '',
+      dockerWorkspacePath: '/github/workspace',
+      engine: 'unity',
+    });
+
+    expect(command).not.toContain('--shm-size');
+  });
+
   it('mounts a custom SSH public keys directory instead of the known_hosts fallback', () => {
     const command = (Docker as any).getLinuxCommand('game-ci/unity-editor-stub:latest', {
       hostOS: 'linux',
@@ -134,11 +151,13 @@ describe('Docker', () => {
       engine: 'unity',
       dockerCpuLimit: '4',
       dockerMemoryLimit: '8192m',
+      dockerShmSize: '1024m',
       dockerIsolationMode: 'process',
     });
 
     expect(command).toContain('--cpus=4');
     expect(command).toContain('--memory=8192m');
+    expect(command).toContain('--shm-size=1024m');
     expect(command).toContain('--isolation=process');
   });
 
diff --git a/src/model/docker.ts b/src/model/docker.ts
index 2bd8dbd..cc87ceb 100644
--- a/src/model/docker.ts
+++ b/src/model/docker.ts
@@ -75,6 +75,7 @@ class Docker {
       useHostNetwork,
       dockerCpuLimit,
       dockerMemoryLimit,
+      dockerShmSize,
     } = options as Options & { commands?: string };
 
     const home = homeDir;
@@ -98,6 +99,7 @@ class Docker {
       sshAgent ? '--env SSH_AUTH_SOCK=/ssh-agent' : '',
       dockerCpuLimit ? `--cpus=${dockerCpuLimit}` : '',
       dockerMemoryLimit ? `--memory=${dockerMemoryLimit}` : '',
+      dockerShmSize ? `--shm-size=${dockerShmSize}` : '',
       useHostNetwork ? '--net=host' : '',
       `--volume "${home}":"/root:z"`,
       `--volume "${currentWorkDir}":"${dockerWorkspacePath}:z"`,
@@ -128,6 +130,7 @@ class Docker {
       engine,
       dockerCpuLimit,
       dockerMemoryLimit,
+      dockerShmSize,
       dockerIsolationMode,
     } = options as Options & { commands?: string };
 
@@ -150,6 +153,7 @@ class Docker {
       `  --env GIT_PRIVATE_TOKEN="${gitPrivateToken}" \``,
       dockerCpuLimit ? `  --cpus=${dockerCpuLimit} \`` : '',
       dockerMemoryLimit ? `  --memory=${dockerMemoryLimit} \`` : '',
+      dockerShmSize ? `  --shm-size=${dockerShmSize} \`` : '',
       dockerIsolationMode ? `  --isolation=${dockerIsolationMode} \`` : '',
       `  --volume="${currentWorkDir}":"c:${dockerWorkspacePath}" \``,
       isUnityDefaultFlow ? `  --volume="${cliStoragePath}/registry-keys":"c:/registry-keys" \`` : '',