diff --git a/.github/workflows/ci-cd.yml b/.github/workflows/ci-cd.yml
index b13075d87..12dd75a69 100644
--- a/.github/workflows/ci-cd.yml
+++ b/.github/workflows/ci-cd.yml
@@ -182,7 +182,7 @@ jobs:
         docker exec slurm bash -c "ls -la /pydra && echo list pydra dir"
         docker exec slurm bash -c "CONFIGURE_OPTS=\"-with-openssl=/opt/openssl\" pyenv install -v ${{ matrix.python-version }}"
         docker exec slurm bash -c "pyenv global ${{ matrix.python-version }}"
-        docker exec slurm bash -c "pip install --upgrade pip && pip install -e /pydra[test,psij] && python -c 'import pydra.engine; print(pydra.utils.__version__)'"
+        docker exec slurm bash -c "pip install --upgrade pip && pip install 'numpy<2' -e /pydra[test,psij] && python -c 'import pydra.engine; print(pydra.utils.__version__)'"
     - name: Run pytest
       run: |
         docker exec slurm bash -c "cd /pydra; pytest pydra/workers/tests/test_worker.py --only-worker=slurm --color=yes"
@@ -315,9 +315,12 @@ jobs:
       with:
         auto-activate-base: true
         activate-environment: ""
+    # We generate dummy aliases so they can be deleted by conda later without throwing an error
     - name: Install MRtrix via Conda
       run: |
-        conda install -c mrtrix3 mrtrix3
+        alias shview='ls'
+        alias mrview='ls'
+        conda install -c conda-forge -c MRtrix3 mrtrix3 libstdcxx-ng
         mrconvert --version
     - name: Set up Python
       uses: actions/setup-python@v5
diff --git a/docs/source/tutorial/7-canonical-form.ipynb b/docs/source/tutorial/7-canonical-form.ipynb
index 428ef217a..d834249fe 100644
--- a/docs/source/tutorial/7-canonical-form.ipynb
+++ b/docs/source/tutorial/7-canonical-form.ipynb
@@ -4,7 +4,7 @@
    "cell_type": "markdown",
    "metadata": {},
    "source": [
-    "# Canonical form and serialisation\n",
+    "# Canonical forms\n",
     "\n",
     "## Canonical task form\n",
     "\n",
@@ -28,7 +28,7 @@
    "cell_type": "markdown",
    "metadata": {},
    "source": [
-    "## Python-tasks\n",
+    "### Python-tasks\n",
     "\n",
     "Python tasks in dataclass form are decorated by `pydra.compose.python.define`\n",
     "with inputs listed as type annotations. Outputs are similarly defined in a nested class\n",
@@ -135,7 +135,7 @@
    "cell_type": "markdown",
    "metadata": {},
    "source": [
-    "## Shell-tasks\n",
+    "### Shell-tasks\n",
     "\n",
     "The canonical form of shell tasks is the same as for Python tasks, except a string `executable`\n",
     "attribute replaces the `function` staticmethod."
@@ -183,7 +183,7 @@
    "cell_type": "markdown",
    "metadata": {},
    "source": [
-    "## Workflow definitions\n",
+    "### Workflow definitions\n",
     "\n",
     "Workflows can also be defined in canonical form, which is the same as for Python tasks\n",
     "but with a staticmethod called `constructor` that constructs the workflow."
@@ -242,7 +242,7 @@
    "cell_type": "markdown",
    "metadata": {},
    "source": [
-    "## Converting to/from dictionaries\n",
+    "## Conversion to/from dictionaries\n",
     "\n",
     "As well as the dataclass-like canonical form, it is also possible to represent all tasks\n",
     "in a nested dictionary form, which could be written to a static file (e.g. in JSON or\n",
diff --git a/pydra/compose/base/field.py b/pydra/compose/base/field.py
index d72f2bfaf..6d620e7d3 100644
--- a/pydra/compose/base/field.py
+++ b/pydra/compose/base/field.py
@@ -229,7 +229,12 @@ def mandatory(self):
 
     @requires.validator
     def _requires_validator(self, _, value):
-        if value and self.type not in (ty.Any, bool) and not is_optional(self.type):
+        if (
+            value
+            and self.type not in (ty.Any, bool)
+            and not is_optional(self.type)
+            and not issubclass(self.type, ty.Sequence)
+        ):
             raise ValueError(
                 f"Fields with requirements must be of optional type (i.e. in union "
                 f"with None) or boolean, not type {self.type} ({self!r})"