diff --git a/requests_html.py b/requests_html.py
index 94a5f22..042adad 100644
--- a/requests_html.py
+++ b/requests_html.py
@@ -681,6 +681,8 @@ class HTMLSession(BaseSession):
     def browser(self):
         if not hasattr(self, "_browser"):
             self.loop = asyncio.get_event_loop()
+            if self.loop.is_running():
+                raise RuntimeError("Cannot use HTMLSession within an existing event loop. Use AsyncHTMLSession instead.")
             self._browser = self.loop.run_until_complete(super().browser)
         return self._browser
 
@@ -711,3 +713,9 @@ class AsyncHTMLSession(BaseSession):
         """ Partial original request func and run it in a thread. """
         func = partial(super().request, *args, **kwargs)
         return self.loop.run_in_executor(self.thread_pool, func)
+
+    async def close(self):
+        """ If a browser was created close it first. """
+        if hasattr(self, "_browser"):
+            await self._browser.close()
+        super().close()
diff --git a/tests/test_requests_html.py b/tests/test_requests_html.py
index 129bd5e..5d583dd 100644
--- a/tests/test_requests_html.py
+++ b/tests/test_requests_html.py
@@ -247,6 +247,15 @@ def test_browser_session():
     # assert count_chromium_process() == 0
 
 
+@pytest.mark.ok
+@pytest.mark.asyncio
+async def test_browser_session_fail():
+    """ HTMLSession.browser should not be call within an existing event loop> """
+    session = HTMLSession()
+    with pytest.raises(RuntimeError):
+        session.browser
+
+
 @pytest.mark.ok
 def test_browser_process():
     for _ in range(3):
@@ -256,6 +265,14 @@ def test_browser_process():
         assert r.html.page == None
 
 
+@pytest.mark.ok
+@pytest.mark.asyncio
+async def test_async_browser_session():
+    session = AsyncHTMLSession()
+    browser = await session.browser
+    assert isinstance(browser, Browser)
+    await session.close()
+
 
 if __name__ == '__main__':
     test_containing()