diff --git a/.github/workflows/pathogen-repo-ci.yaml b/.github/workflows/pathogen-repo-ci.yaml
index aaa8480..ff76740 100644
--- a/.github/workflows/pathogen-repo-ci.yaml
+++ b/.github/workflows/pathogen-repo-ci.yaml
@@ -68,6 +68,7 @@ on:
           The `BUILD_DIR` for `nextstrain build $BUILD_DIR`.
           Example data is expected to be in `$BUILD_DIR/example_data/`
           Defaults to the root of the workflow repo.
+          Directory string must not end in a slash.
         type: string
         default: ${{ github.workspace }}
         required: false