diff --git a/src/spec-node/utils.ts b/src/spec-node/utils.ts
index e6cf6980f..c530aa2b6 100644
--- a/src/spec-node/utils.ts
+++ b/src/spec-node/utils.ts
@@ -19,11 +19,12 @@ import { ShellServer } from '../spec-common/shellServer';
 import { inspectContainer, inspectContainers, inspectImage, getEvents, listContainers, ContainerDetails, DockerCLIParameters, dockerExecFunction, dockerPtyCLI, dockerPtyExecFunction, toDockerImageName, DockerComposeCLI, ImageDetails, dockerCLI, removeContainer, CLIVariant } from '../spec-shutdown/dockerUtils';
 import { getRemoteWorkspaceFolder } from './dockerCompose';
 import { findGitRootFolder } from '../spec-common/git';
+import { substitute } from '../spec-common/variableSubstitution';
 import { parentURI, uriToFsPath } from '../spec-configuration/configurationCommonUtils';
 import { DevContainerConfig, DevContainerFromDockerfileConfig, getConfigFilePath, getDockerfilePath } from '../spec-configuration/configuration';
 import { StringDecoder } from 'string_decoder';
 import { Event } from '../spec-utils/event';
-import { Mount } from '../spec-configuration/containerFeaturesConfiguration';
+import { Mount, parseMount } from '../spec-configuration/containerFeaturesConfiguration';
 import { PackageConfiguration } from '../spec-utils/product';
 import { ImageMetadataEntry, MergedDevContainerConfig } from './imageMetadata';
 import { getImageIndexEntryForPlatform, getManifest, getRef } from '../spec-configuration/containerCollectionsOCI';
@@ -417,7 +418,7 @@ export async function getWorkspaceConfiguration(cliHost: CLIHost, workspace: Wor
 	}
 	let { workspaceFolder, workspaceMount } = config;
 	let additionalMountString: string | undefined;
-	if (workspace && (!workspaceFolder || !('workspaceMount' in config))) {
+	if (workspace && (!workspaceFolder || !('workspaceMount' in config) || (mountWorkspaceGitRoot && mountGitWorktreeCommonDir))) {
 		const hostMountFolder = await getHostMountFolder(cliHost, workspace.rootFolderPath, mountWorkspaceGitRoot, output);
 
 		// Check if .git is a file (worktree) with a relative gitdir path
@@ -439,9 +440,17 @@ export async function getWorkspaceConfiguration(cliHost: CLIHost, workspace: Wor
 							segments.unshift(cliHost.path.basename(current));
 						}
 						containerMountFolder = path.posix.join('/workspaces', ...segments);
+						// A custom workspaceMount defines where the worktree is mounted in the container; resolve the
+						// common dir relative to that (substituted) target so the relative gitdir resolves correctly.
+						// additionalMountString is not part of the later substitution pass, so substitute here.
+						// Otherwise fall back to the computed containerMountFolder.
+						const customMountTarget = 'workspaceMount' in config && config.workspaceMount ?
+							substitute({ platform: cliHost.platform, localWorkspaceFolder: workspace.rootFolderPath, env: cliHost.env }, parseMount(config.workspaceMount)).target :
+							undefined;
+						const worktreeContainerFolder = customMountTarget || containerMountFolder;
 						// Calculate where the common dir should be mounted in the container
 						const containerGitdir = cliHost.platform === 'win32' ? gitdir.replace(/\\/g, '/') : gitdir;
-						const containerGitCommonDir = path.posix.resolve(containerMountFolder, containerGitdir, '..', '..');
+						const containerGitCommonDir = path.posix.resolve(worktreeContainerFolder, containerGitdir, '..', '..');
 						const cons = cliHost.platform !== 'linux' ? `,consistency=${consistency || 'consistent'}` : '';
 						const srcQuote = gitCommonDir.indexOf(',') !== -1 ? '"' : '';
 						const tgtQuote = containerGitCommonDir.indexOf(',') !== -1 ? '"' : '';
diff --git a/src/test/workspaceConfiguration.test.ts b/src/test/workspaceConfiguration.test.ts
index 1e0b7e992..550775519 100644
--- a/src/test/workspaceConfiguration.test.ts
+++ b/src/test/workspaceConfiguration.test.ts
@@ -330,6 +330,154 @@ describe('getWorkspaceConfiguration', function () {
 
 			});
 
+			describe('git worktree with custom workspaceMount', function () {
+
+				it('should add common dir mount when a custom workspaceMount and workspaceFolder are set', async () => {
+					const p = {
+						linux: { worktreePath: '/home/user/worktrees/feature', gitFile: '/home/user/worktrees/feature/.git', gitdir: 'gitdir: ../main/.git/worktrees/feature', mainGitPath: '/home/user/worktrees/main/.git', consistency: '' },
+						darwin: { worktreePath: '/Users/user/worktrees/feature', gitFile: '/Users/user/worktrees/feature/.git', gitdir: 'gitdir: ../main/.git/worktrees/feature', mainGitPath: '/Users/user/worktrees/main/.git', consistency: ',consistency=consistent' },
+						win32: { worktreePath: 'C:\\Users\\user\\worktrees\\feature', gitFile: 'C:\\Users\\user\\worktrees\\feature\\.git', gitdir: 'gitdir: ../main/.git/worktrees/feature', mainGitPath: 'C:\\Users\\user\\worktrees\\main\\.git', consistency: ',consistency=consistent' },
+					}[platform];
+
+					const cliHost = createMockCLIHost({
+						platform,
+						files: {
+							[p.gitFile]: p.gitdir
+						}
+					});
+					const workspace = createWorkspace(p.worktreePath);
+
+					const result = await getWorkspaceConfiguration(
+						cliHost,
+						workspace,
+						{ workspaceMount: 'type=bind,source=/host/wt,target=/workspace', workspaceFolder: '/workspace' },
+						true,
+						true,
+						nullLog
+					);
+
+					// The custom workspaceMount/workspaceFolder are respected unchanged, and the common dir is
+					// still mounted, with its target resolved relative to the custom mount target (/workspace).
+					assert.strictEqual(result.workspaceMount, 'type=bind,source=/host/wt,target=/workspace');
+					assert.strictEqual(result.workspaceFolder, '/workspace');
+					assert.strictEqual(result.additionalMountString, `type=bind,source=${p.mainGitPath},target=/main/.git${p.consistency}`);
+				});
+
+				it('should substitute variables in the custom workspaceMount target', async () => {
+					const p = {
+						linux: { worktreePath: '/home/user/worktrees/feature', gitFile: '/home/user/worktrees/feature/.git', gitdir: 'gitdir: ../main/.git/worktrees/feature', mainGitPath: '/home/user/worktrees/main/.git', consistency: '' },
+						darwin: { worktreePath: '/Users/user/worktrees/feature', gitFile: '/Users/user/worktrees/feature/.git', gitdir: 'gitdir: ../main/.git/worktrees/feature', mainGitPath: '/Users/user/worktrees/main/.git', consistency: ',consistency=consistent' },
+						win32: { worktreePath: 'C:\\Users\\user\\worktrees\\feature', gitFile: 'C:\\Users\\user\\worktrees\\feature\\.git', gitdir: 'gitdir: ../main/.git/worktrees/feature', mainGitPath: 'C:\\Users\\user\\worktrees\\main\\.git', consistency: ',consistency=consistent' },
+					}[platform];
+
+					const cliHost = createMockCLIHost({
+						platform,
+						files: {
+							[p.gitFile]: p.gitdir
+						}
+					});
+					const workspace = createWorkspace(p.worktreePath);
+
+					const result = await getWorkspaceConfiguration(
+						cliHost,
+						workspace,
+						{ workspaceMount: 'type=bind,source=${localWorkspaceFolder},target=/workspaces/${localWorkspaceFolderBasename}', workspaceFolder: '/workspaces/feature' },
+						true,
+						true,
+						nullLog
+					);
+
+					// ${localWorkspaceFolderBasename} in the target is substituted before resolving the common dir.
+					assert.strictEqual(result.additionalMountString, `type=bind,source=${p.mainGitPath},target=/workspaces/main/.git${p.consistency}`);
+				});
+
+				it('should not add common dir mount when mountGitWorktreeCommonDir is false', async () => {
+					const p = {
+						linux: { worktreePath: '/home/user/worktrees/feature', gitFile: '/home/user/worktrees/feature/.git', gitdir: 'gitdir: ../main/.git/worktrees/feature' },
+						darwin: { worktreePath: '/Users/user/worktrees/feature', gitFile: '/Users/user/worktrees/feature/.git', gitdir: 'gitdir: ../main/.git/worktrees/feature' },
+						win32: { worktreePath: 'C:\\Users\\user\\worktrees\\feature', gitFile: 'C:\\Users\\user\\worktrees\\feature\\.git', gitdir: 'gitdir: ../main/.git/worktrees/feature' },
+					}[platform];
+
+					const cliHost = createMockCLIHost({
+						platform,
+						files: {
+							[p.gitFile]: p.gitdir
+						}
+					});
+					const workspace = createWorkspace(p.worktreePath);
+
+					const result = await getWorkspaceConfiguration(
+						cliHost,
+						workspace,
+						{ workspaceMount: 'type=bind,source=/host/wt,target=/workspace', workspaceFolder: '/workspace' },
+						true,
+						false,
+						nullLog
+					);
+
+					assert.strictEqual(result.workspaceMount, 'type=bind,source=/host/wt,target=/workspace');
+					assert.strictEqual(result.workspaceFolder, '/workspace');
+					assert.isUndefined(result.additionalMountString);
+				});
+
+				it('should not add common dir mount when .git is not a worktree file', async () => {
+					const p = {
+						linux: { projectPath: '/home/user/project' },
+						darwin: { projectPath: '/Users/user/project' },
+						win32: { projectPath: 'C:\\Users\\user\\project' },
+					}[platform];
+
+					const cliHost = createMockCLIHost({
+						platform,
+						files: {}
+					});
+					const workspace = createWorkspace(p.projectPath);
+
+					const result = await getWorkspaceConfiguration(
+						cliHost,
+						workspace,
+						{ workspaceMount: 'type=bind,source=/host/wt,target=/workspace', workspaceFolder: '/workspace' },
+						true,
+						true,
+						nullLog
+					);
+
+					assert.strictEqual(result.workspaceMount, 'type=bind,source=/host/wt,target=/workspace');
+					assert.strictEqual(result.workspaceFolder, '/workspace');
+					assert.isUndefined(result.additionalMountString);
+				});
+
+				it('should add common dir mount for a worktree nested inside the main repo', async () => {
+					const p = {
+						linux: { worktreePath: '/home/user/main/wt', gitFile: '/home/user/main/wt/.git', gitdir: 'gitdir: ../.git/worktrees/wt', mainGitPath: '/home/user/main/.git', consistency: '' },
+						darwin: { worktreePath: '/Users/user/main/wt', gitFile: '/Users/user/main/wt/.git', gitdir: 'gitdir: ../.git/worktrees/wt', mainGitPath: '/Users/user/main/.git', consistency: ',consistency=consistent' },
+						win32: { worktreePath: 'C:\\Users\\user\\main\\wt', gitFile: 'C:\\Users\\user\\main\\wt\\.git', gitdir: 'gitdir: ../.git/worktrees/wt', mainGitPath: 'C:\\Users\\user\\main\\.git', consistency: ',consistency=consistent' },
+					}[platform];
+
+					const cliHost = createMockCLIHost({
+						platform,
+						files: {
+							[p.gitFile]: p.gitdir
+						}
+					});
+					const workspace = createWorkspace(p.worktreePath);
+
+					const result = await getWorkspaceConfiguration(
+						cliHost,
+						workspace,
+						{ workspaceMount: 'type=bind,source=/host/wt,target=/workspace', workspaceFolder: '/workspace' },
+						true,
+						true,
+						nullLog
+					);
+
+					// Worktree nested under the main repo: gitdir points up one level; the common dir resolves to
+					// a root-level target inside the container, consistent with how git resolves it there.
+					assert.strictEqual(result.additionalMountString, `type=bind,source=${p.mainGitPath},target=/.git${p.consistency}`);
+				});
+
+			});
+
 			describe('git root in parent folder', function () {
 
 				it('should mount from git root when .git/config is in parent folder', async () => {