diff --git a/crawl4ai/browser_manager.py b/crawl4ai/browser_manager.py
index f4ab0aa32..6f7982271 100644
--- a/crawl4ai/browser_manager.py
+++ b/crawl4ai/browser_manager.py
@@ -157,8 +157,25 @@ def __init__(
             host (str): Host for debugging the browser. Default: "localhost".
             debugging_port (int): Port for debugging the browser. Default: 9222.
             cdp_url (str or None): CDP URL to connect to the browser. Default: None.
-            browser_config (BrowserConfig): Configuration object containing all browser settings. Default: None.
+            browser_config (BrowserConfig): Configuration object carrying the same settings. When
+                                            given it is used as-is and the individual arguments
+                                            above are ignored; when omitted one is built from
+                                            them. Default: None.
         """
+        if browser_config is None:
+            # Every attribute below is read off `browser_config`, so without this the
+            # documented all-arguments form raised
+            # `AttributeError: 'NoneType' object has no attribute 'browser_type'`, and the
+            # arguments themselves reached nothing.
+            browser_config = BrowserConfig(
+                browser_type=browser_type,
+                headless=headless,
+                user_data_dir=user_data_dir,
+                host=host,
+                debugging_port=debugging_port,
+                cdp_url=cdp_url,
+            )
+
         self.browser_type = browser_config.browser_type
         self.user_data_dir = browser_config.user_data_dir
         self.headless = browser_config.headless
diff --git a/tests/unit/test_managed_browser_arguments.py b/tests/unit/test_managed_browser_arguments.py
new file mode 100644
index 000000000..5ca9f06cd
--- /dev/null
+++ b/tests/unit/test_managed_browser_arguments.py
@@ -0,0 +1,66 @@
+"""`ManagedBrowser` reads every setting off `browser_config`.
+
+Without one, that raised `AttributeError: 'NoneType' object has no attribute
+'browser_type'` for the documented all-arguments form, which is how
+`BrowserProfiler.launch_builtin_browser` constructs it — so `crwl browser start`
+and `crwl browser restart` could not start a browser at all.
+"""
+
+import pytest
+
+from crawl4ai.async_configs import BrowserConfig
+from crawl4ai.browser_manager import ManagedBrowser
+
+
+def test_defaults_construct_without_a_config():
+    browser = ManagedBrowser()
+
+    assert browser.browser_type == "chromium"
+    assert browser.debugging_port == 9222
+    assert browser.host == "localhost"
+
+
+def test_launch_builtin_browser_argument_shape_constructs():
+    """The exact call `BrowserProfiler.launch_builtin_browser` makes."""
+    browser = ManagedBrowser(
+        browser_type="chromium",
+        user_data_dir="/tmp/crawl4ai-builtin",
+        headless=True,
+        logger=None,
+        debugging_port=9333,
+    )
+
+    assert browser.user_data_dir == "/tmp/crawl4ai-builtin"
+    assert browser.debugging_port == 9333
+
+
+@pytest.mark.parametrize(
+    ("kwargs", "attribute", "expected"),
+    [
+        ({"browser_type": "firefox"}, "browser_type", "firefox"),
+        ({"user_data_dir": "/tmp/profile"}, "user_data_dir", "/tmp/profile"),
+        ({"headless": False}, "headless", False),
+        ({"host": "0.0.0.0"}, "host", "0.0.0.0"),
+        ({"debugging_port": 9333}, "debugging_port", 9333),
+        ({"cdp_url": "http://localhost:9444"}, "cdp_url", "http://localhost:9444"),
+    ],
+)
+def test_each_argument_reaches_the_instance(kwargs, attribute, expected):
+    assert getattr(ManagedBrowser(**kwargs), attribute) == expected
+
+
+def test_a_supplied_config_still_wins():
+    """Existing callers pass both; the config is the source of truth and stays so."""
+    config = BrowserConfig(browser_type="chromium", debugging_port=9222, headless=True)
+
+    browser = ManagedBrowser(
+        browser_type="firefox",
+        debugging_port=9333,
+        headless=False,
+        browser_config=config,
+    )
+
+    assert browser.browser_type == "chromium"
+    assert browser.debugging_port == 9222
+    assert browser.headless is True
+    assert browser.browser_config is config