diff --git a/spacy/cli/_util.py b/spacy/cli/_util.py
index df98e711f..ce9c2a5d3 100644
--- a/spacy/cli/_util.py
+++ b/spacy/cli/_util.py
@@ -1,5 +1,5 @@
 from typing import Dict, Any, Union, List, Optional, Tuple, Iterable
-from typing import TYPE_CHECKING, overload
+from typing import TYPE_CHECKING, overload, cast
 import sys
 import shutil
 from pathlib import Path
@@ -151,6 +151,7 @@ def load_project_config(
         config = srsly.read_yaml(config_path)
     except ValueError as e:
         msg.fail(invalid_err, e, exits=1)
+    print(config)
     errors = validate(ProjectConfigSchema, config)
     if errors:
         msg.fail(invalid_err)
@@ -221,18 +222,9 @@ def validate_project_commands(config: Dict[str, Any]) -> None:
 
     config (Dict[str, Any]): The loaded config.
     """
-    command_names = [cmd["name"] for cmd in config.get("commands", [])]
-    workflows = config.get("workflows", {})
-    duplicates = set([cmd for cmd in command_names if command_names.count(cmd) > 1])
-    if duplicates:
-        err = f"Duplicate commands defined in {PROJECT_FILE}: {', '.join(duplicates)}"
-        msg.fail(err, exits=1)
-    for workflow_name, workflow_steps in workflows.items():
-        if workflow_name in command_names:
-            err = f"Can't use workflow name '{workflow_name}': name already exists as a command"
-            msg.fail(err, exits=1)
-        for step in workflow_steps:
-            if step not in command_names:
+
+    def verify_workflow_step(step: str):
+        if step not in command_names:
                 msg.fail(
                     f"Unknown command specified in workflow '{workflow_name}': {step}",
                     f"Workflows can only refer to commands defined in the 'commands' "
@@ -240,6 +232,30 @@ def validate_project_commands(config: Dict[str, Any]) -> None:
                     exits=1,
                 )
 
+    command_names = [cmd["name"] for cmd in config.get("commands", [])]
+    workflows = config.get("workflows", {})
+    duplicates = set([cmd for cmd in command_names if command_names.count(cmd) > 1])
+    if duplicates:
+        err = f"Duplicate commands defined in {PROJECT_FILE}: {', '.join(duplicates)}"
+        msg.fail(err, exits=1)
+    for workflow_name, workflow_step_or_lists in workflows.items():
+        if workflow_name in command_names:
+            err = f"Can't use workflow name '{workflow_name}': name already exists as a command"
+            msg.fail(err, exits=1)
+        for step_or_list in workflow_step_or_lists:
+            if isinstance(step_or_list, str):
+                verify_workflow_step(step_or_list)
+            else:
+                workflow_list = cast(List[str], step_or_list)
+                if len(workflow_list) < 2:
+                    msg.fail(
+                    f"Invalid multiprocessing group within '{workflow_name}'",
+                    f"A multiprocessing group must reference at least two commands.",
+                    exits=1,
+                )
+                for step in workflow_list:
+                    verify_workflow_step(step)
+        
 
 def get_hash(data, exclude: Iterable[str] = tuple()) -> str:
     """Get the hash for a JSON-serializable object.
diff --git a/spacy/schemas.py b/spacy/schemas.py
index 1dfd8ee85..5a9391640 100644
--- a/spacy/schemas.py
+++ b/spacy/schemas.py
@@ -458,8 +458,8 @@ class ProjectConfigSchema(BaseModel):
     vars: Dict[StrictStr, Any] = Field({}, title="Optional variables to substitute in commands")
     env: Dict[StrictStr, Any] = Field({}, title="Optional variable names to substitute in commands, mapped to environment variable names")
     assets: List[Union[ProjectConfigAssetURL, ProjectConfigAssetGit]] = Field([], title="Data assets")
-    workflows: Dict[StrictStr, List[StrictStr]] = Field({}, title="Named workflows, mapped to list of project commands to run in order")
-    commands: List[ProjectConfigCommand] = Field([], title="Project command shortucts")
+    workflows: Dict[StrictStr, List[Union[StrictStr, List[StrictStr]]]] = Field({}, title="Named workflows, mapped to list of project commands to run in order")
+    commands: List[ProjectConfigCommand] = Field([], title="Project command shortcuts")
     title: Optional[str] = Field(None, title="Project title")
     spacy_version: Optional[StrictStr] = Field(None, title="spaCy version range that the project is compatible with")
     # fmt: on
diff --git a/spacy/tests/test_cli.py b/spacy/tests/test_cli.py
index 0fa6f5670..86583b1ab 100644
--- a/spacy/tests/test_cli.py
+++ b/spacy/tests/test_cli.py
@@ -421,6 +421,42 @@ def test_project_config_interpolation(int_value):
         substitute_project_variables(project)
 
 
+def test_project_config_multiprocessing_good_case():
+    project = {
+        "commands": [
+            {"name": "command1", "script": ["echo", "command1"]},
+            {"name": "command2", "script": ["echo", "command2"]},
+            {"name": "command3", "script": ["echo", "command3"]},
+        ],
+        "workflows": {"all": ["command1", ["command2", "command3"]]},
+    }
+    with make_tempdir() as d:
+        srsly.write_yaml(d / "project.yml", project)
+        load_project_config(d)
+
+
+@pytest.mark.parametrize(
+    "workflows",
+    [
+        {"all": ["command1", ["command2"], "command3"]},
+        {"all": ["command1", ["command2", "command4"]]},
+    ],
+)
+def test_project_config_multiprocessing_bad_case(workflows):
+    project = {
+        "commands": [
+            {"name": "command1", "script": ["echo", "command1"]},
+            {"name": "command2", "script": ["echo", "command2"]},
+            {"name": "command3", "script": ["echo", "command3"]},
+        ],
+        "workflows": workflows,
+    }
+    with make_tempdir() as d:
+        srsly.write_yaml(d / "project.yml", project)
+        with pytest.raises(SystemExit):
+            load_project_config(d)
+
+
 @pytest.mark.parametrize(
     "greeting",
     [342, "everyone", "tout le monde", pytest.param("42", marks=pytest.mark.xfail)],