diff --git a/action.yml b/action.yml
index 4c910ef35..3f5bcc074 100644
--- a/action.yml
+++ b/action.yml
@@ -9,6 +9,10 @@ inputs:
     description: 'Folder to place the outputs in, defaults to "wheelhouse"'
     required: false
     default: wheelhouse
+  config-file:
+    description: 'File containing the config, defaults to {package}/pyproject.toml'
+    required: false
+    default: ''
 branding:
   icon: package
   color: yellow
@@ -24,5 +28,6 @@ runs:
         cibuildwheel
         ${{ inputs.package-dir }}
         --output-dir ${{ inputs.output-dir }}
+        --config-file "${{ input.config-file }}"
         2>&1
       shell: bash
diff --git a/cibuildwheel/__main__.py b/cibuildwheel/__main__.py
index c6a532f95..a04d3e82b 100644
--- a/cibuildwheel/__main__.py
+++ b/cibuildwheel/__main__.py
@@ -57,14 +57,15 @@ def main() -> None:
 
     parser.add_argument(
         "--output-dir",
-        help="Destination folder for the wheels.",
+        help="Destination folder for the wheels. Default: wheelhouse.",
     )
 
     parser.add_argument(
         "--config-file",
+        default="",
         help="""
-            TOML config file for cibuildwheel. Defaults to pyproject.toml, but
-            can be overridden with this option.
+            TOML config file. Default: "", meaning {package}/pyproject.toml,
+            if it exists.
         """,
     )
 
diff --git a/cibuildwheel/options.py b/cibuildwheel/options.py
index 902b64fa5..9a207e9e0 100644
--- a/cibuildwheel/options.py
+++ b/cibuildwheel/options.py
@@ -42,7 +42,7 @@ class CommandLineArguments:
     platform: Literal["auto", "linux", "macos", "windows"]
     archs: Optional[str]
     output_dir: Optional[str]
-    config_file: Optional[str]
+    config_file: str
     package_dir: str
     print_build_identifiers: bool
     allow_empty: bool
@@ -335,8 +335,9 @@ def __init__(self, platform: PlatformName, command_line_arguments: CommandLineAr
     def config_file_path(self) -> Optional[Path]:
         args = self.command_line_arguments
 
-        if args.config_file is not None:
+        if args.config_file:
             return Path(args.config_file.format(package=args.package_dir))
+
         # return pyproject.toml, if it's available
         pyproject_toml_path = Path(args.package_dir) / "pyproject.toml"
         if pyproject_toml_path.exists():
diff --git a/unit_test/utils.py b/unit_test/utils.py
index 0f7359166..61833fa2d 100644
--- a/unit_test/utils.py
+++ b/unit_test/utils.py
@@ -7,7 +7,7 @@ def get_default_command_line_arguments() -> CommandLineArguments:
     defaults.platform = "auto"
     defaults.allow_empty = False
     defaults.archs = None
-    defaults.config_file = None
+    defaults.config_file = ""
     defaults.output_dir = None
     defaults.package_dir = "."
     defaults.prerelease_pythons = False