diff --git a/crates/vp_cli_snapshots/tests/cli_snapshots/fixtures/migration_workspace_member_target/package.json b/crates/vp_cli_snapshots/tests/cli_snapshots/fixtures/migration_workspace_member_target/package.json
new file mode 100644
index 0000000000..6a2f1757bc
--- /dev/null
+++ b/crates/vp_cli_snapshots/tests/cli_snapshots/fixtures/migration_workspace_member_target/package.json
@@ -0,0 +1,7 @@
+{
+  "name": "workspace-root",
+  "private": true,
+  "workspaces": [
+    "vendor/*"
+  ]
+}
diff --git a/crates/vp_cli_snapshots/tests/cli_snapshots/fixtures/migration_workspace_member_target/snapshots.toml b/crates/vp_cli_snapshots/tests/cli_snapshots/fixtures/migration_workspace_member_target/snapshots.toml
new file mode 100644
index 0000000000..81639391ac
--- /dev/null
+++ b/crates/vp_cli_snapshots/tests/cli_snapshots/fixtures/migration_workspace_member_target/snapshots.toml
@@ -0,0 +1,64 @@
+[[case]]
+name = "migration_workspace_member_cwd"
+vp = "global"
+cwd = "vendor/sub"
+steps = [
+  { argv = [
+    "vp",
+    "migrate",
+    "--no-interactive",
+    "--no-agent",
+    "--no-editor",
+    "--no-hooks",
+  ], comment = "vp migrate rejects a workspace member before it changes files", continue-on-failure = true },
+  { argv = [
+    "vpt",
+    "print-file",
+    "../../package.json",
+  ], comment = "the workspace root package.json is unchanged", continue-on-failure = true },
+  { argv = [
+    "vpt",
+    "print-file",
+    "package.json",
+  ], comment = "the workspace member package.json is unchanged", continue-on-failure = true },
+  { argv = [
+    "vpt",
+    "stat-file",
+    "../../pnpm-workspace.yaml",
+    "--assert",
+    "missing",
+  ], comment = "the migration created no package-manager files at the workspace root" },
+]
+
+[[case]]
+name = "migration_workspace_member_explicit_path"
+vp = "global"
+cwd = "vendor/sub"
+steps = [
+  { argv = [
+    "vp",
+    "migrate",
+    ".",
+    "--no-interactive",
+    "--no-agent",
+    "--no-editor",
+    "--no-hooks",
+  ], comment = "vp migrate rejects an explicit workspace-member target before it changes files", continue-on-failure = true },
+  { argv = [
+    "vpt",
+    "print-file",
+    "../../package.json",
+  ], comment = "the workspace root package.json is unchanged", continue-on-failure = true },
+  { argv = [
+    "vpt",
+    "print-file",
+    "package.json",
+  ], comment = "the workspace member package.json is unchanged", continue-on-failure = true },
+  { argv = [
+    "vpt",
+    "stat-file",
+    "../../pnpm-workspace.yaml",
+    "--assert",
+    "missing",
+  ], comment = "the migration created no package-manager files at the workspace root" },
+]
diff --git a/crates/vp_cli_snapshots/tests/cli_snapshots/fixtures/migration_workspace_member_target/snapshots/migration_workspace_member_cwd.md b/crates/vp_cli_snapshots/tests/cli_snapshots/fixtures/migration_workspace_member_target/snapshots/migration_workspace_member_cwd.md
new file mode 100644
index 0000000000..bb5d853f6c
--- /dev/null
+++ b/crates/vp_cli_snapshots/tests/cli_snapshots/fixtures/migration_workspace_member_target/snapshots/migration_workspace_member_cwd.md
@@ -0,0 +1,49 @@
+# migration_workspace_member_cwd
+
+## `vp migrate --no-interactive --no-agent --no-editor --no-hooks`
+
+vp migrate rejects a workspace member before it changes files
+
+**Exit code:** 1
+
+```
+VITE+ - The Unified Toolchain for the Web
+
+Vite+ cannot migrate a workspace member. Run `vp migrate` from the workspace root at <workspace>.
+```
+
+## `vpt print-file ../../package.json`
+
+the workspace root package.json is unchanged
+
+```
+{
+  "name": "workspace-root",
+  "private": true,
+  "workspaces": [
+    "vendor/*"
+  ]
+}
+```
+
+## `vpt print-file package.json`
+
+the workspace member package.json is unchanged
+
+```
+{
+  "name": "workspace-member",
+  "private": true,
+  "devDependencies": {
+    "vitest": "<version>"
+  }
+}
+```
+
+## `vpt stat-file ../../pnpm-workspace.yaml --assert missing`
+
+the migration created no package-manager files at the workspace root
+
+```
+../../pnpm-workspace.yaml: missing
+```
diff --git a/crates/vp_cli_snapshots/tests/cli_snapshots/fixtures/migration_workspace_member_target/snapshots/migration_workspace_member_explicit_path.md b/crates/vp_cli_snapshots/tests/cli_snapshots/fixtures/migration_workspace_member_target/snapshots/migration_workspace_member_explicit_path.md
new file mode 100644
index 0000000000..5857314458
--- /dev/null
+++ b/crates/vp_cli_snapshots/tests/cli_snapshots/fixtures/migration_workspace_member_target/snapshots/migration_workspace_member_explicit_path.md
@@ -0,0 +1,49 @@
+# migration_workspace_member_explicit_path
+
+## `vp migrate . --no-interactive --no-agent --no-editor --no-hooks`
+
+vp migrate rejects an explicit workspace-member target before it changes files
+
+**Exit code:** 1
+
+```
+VITE+ - The Unified Toolchain for the Web
+
+Vite+ cannot migrate a workspace member. Run `vp migrate` from the workspace root at <workspace>.
+```
+
+## `vpt print-file ../../package.json`
+
+the workspace root package.json is unchanged
+
+```
+{
+  "name": "workspace-root",
+  "private": true,
+  "workspaces": [
+    "vendor/*"
+  ]
+}
+```
+
+## `vpt print-file package.json`
+
+the workspace member package.json is unchanged
+
+```
+{
+  "name": "workspace-member",
+  "private": true,
+  "devDependencies": {
+    "vitest": "<version>"
+  }
+}
+```
+
+## `vpt stat-file ../../pnpm-workspace.yaml --assert missing`
+
+the migration created no package-manager files at the workspace root
+
+```
+../../pnpm-workspace.yaml: missing
+```
diff --git a/crates/vp_cli_snapshots/tests/cli_snapshots/fixtures/migration_workspace_member_target/vendor/sub/package.json b/crates/vp_cli_snapshots/tests/cli_snapshots/fixtures/migration_workspace_member_target/vendor/sub/package.json
new file mode 100644
index 0000000000..96df63ca31
--- /dev/null
+++ b/crates/vp_cli_snapshots/tests/cli_snapshots/fixtures/migration_workspace_member_target/vendor/sub/package.json
@@ -0,0 +1,7 @@
+{
+  "name": "workspace-member",
+  "private": true,
+  "devDependencies": {
+    "vitest": "4.1.10"
+  }
+}
diff --git a/docs/guide/migrate.md b/docs/guide/migrate.md
index 9de7c63958..a9243c27d7 100644
--- a/docs/guide/migrate.md
+++ b/docs/guide/migrate.md
@@ -22,6 +22,9 @@ The positional `PATH` argument is optional.
 
 - If omitted, `vp migrate` migrates the current directory
 - If provided, it migrates that target directory instead
+- For a monorepo, the target must be the workspace root. Vite+ cannot
+  migrate one workspace member, because migration updates the package-manager
+  configuration, the catalogs, and the lockfiles that all members share.
 
 ```bash
 vp migrate
diff --git a/packages/cli/src/migration/bin.ts b/packages/cli/src/migration/bin.ts
index d856ef8d9d..75a1b5148c 100644
--- a/packages/cli/src/migration/bin.ts
+++ b/packages/cli/src/migration/bin.ts
@@ -1044,6 +1044,15 @@ async function main() {
   printHeader();
 
   const workspaceInfoOptional = await detectWorkspace(projectPath);
+  if (
+    workspaceInfoOptional.isMonorepo &&
+    path.resolve(projectPath) !== path.resolve(workspaceInfoOptional.rootDir)
+  ) {
+    cancelAndExit(
+      `Vite+ cannot migrate a workspace member. Run \`vp migrate\` from the workspace root at ${workspaceInfoOptional.rootDir}.`,
+      1,
+    );
+  }
   const initialChangedPaths = await collectChangedFormatPaths(workspaceInfoOptional.rootDir);
   const preExistingChangedPaths = initialChangedPaths ? new Set(initialChangedPaths) : undefined;
   const resolvedPackageManager = workspaceInfoOptional.packageManager ?? 'unknown';