diff --git a/.github/workflows/downgrade.yml b/.github/workflows/downgrade.yml
index 9c08d41..bd63fe1 100644
--- a/.github/workflows/downgrade.yml
+++ b/.github/workflows/downgrade.yml
@@ -23,6 +23,11 @@ on:
         default: "."
         required: false
         type: string
+      project:
+        description: "Value passed to --project for build & test (e.g. a workspace submodule or lib/X). Default '@.' builds/tests the repo root."
+        default: "@."
+        required: false
+        type: string
       mode:
         description: "julia-downgrade-compat mode: deps (direct), alldeps (deps+weakdeps), weakdeps, or forcedeps (strict lower-bound verification). Empty uses the action default."
         default: ""
@@ -62,9 +67,12 @@ jobs:
           mode: "${{ inputs.mode }}"
 
       - uses: julia-actions/julia-buildpkg@v1
+        with:
+          project: "${{ inputs.project }}"
 
       - uses: julia-actions/julia-runtest@v1
         with:
+          project: "${{ inputs.project }}"
           allow_reresolve: "${{ inputs.allow-reresolve }}"
         env:
           GROUP: "${{ inputs.group }}"
diff --git a/README.md b/README.md
index 574f172..bbec9cb 100644
--- a/README.md
+++ b/README.md
@@ -225,6 +225,7 @@ to catch under-specified `[compat]` lower bounds.
 | `group` | string | `""` | Test group. |
 | `skip` | string | `"Pkg,TOML"` | Comma-separated deps to skip when downgrading. |
 | `projects` | string | `"."` | Comma-separated project dirs to downgrade. |
+| `project` | string | `"@."` | `--project` for build/test (a workspace submodule or `lib/X`); default tests the repo root. |
 | `allow-reresolve` | boolean | `false` | Let Pkg relax the downgraded env when running tests. |
 | `self-hosted` / `os` | | `false` / `ubuntu-latest` | Runner selection. |