diff --git a/httpcore/_async/connection_pool.py b/httpcore/_async/connection_pool.py
index 5541689..e6c4ef6 100644
--- a/httpcore/_async/connection_pool.py
+++ b/httpcore/_async/connection_pool.py
@@ -301,19 +301,11 @@ class AsyncConnectionPool(AsyncRequestInterface):
         Close any connections in the pool.
         """
         async with self._pool_lock:
-            requests_still_in_flight = len(self._requests)
-
             for connection in self._pool:
                 await connection.aclose()
             self._pool = []
             self._requests = []
 
-            if requests_still_in_flight:
-                raise RuntimeError(
-                    f"The connection pool was closed while {requests_still_in_flight} "
-                    f"HTTP requests/responses were still in-flight."
-                )
-
     async def __aenter__(self) -> "AsyncConnectionPool":
         return self
 
diff --git a/httpcore/_sync/connection_pool.py b/httpcore/_sync/connection_pool.py
index 020893d..53536d0 100644
--- a/httpcore/_sync/connection_pool.py
+++ b/httpcore/_sync/connection_pool.py
@@ -301,19 +301,11 @@ class ConnectionPool(RequestInterface):
         Close any connections in the pool.
         """
         with self._pool_lock:
-            requests_still_in_flight = len(self._requests)
-
             for connection in self._pool:
                 connection.close()
             self._pool = []
             self._requests = []
 
-            if requests_still_in_flight:
-                raise RuntimeError(
-                    f"The connection pool was closed while {requests_still_in_flight} "
-                    f"HTTP requests/responses were still in-flight."
-                )
-
     def __enter__(self) -> "ConnectionPool":
         return self
 
diff --git a/httpcore/backends/asyncio.py b/httpcore/backends/asyncio.py
index 3b8abf1..23f7dce 100644
--- a/httpcore/backends/asyncio.py
+++ b/httpcore/backends/asyncio.py
@@ -26,6 +26,7 @@ class AsyncIOStream(AsyncNetworkStream):
         exc_map = {
             TimeoutError: ReadTimeout,
             anyio.BrokenResourceError: ReadError,
+            anyio.ClosedResourceError: ReadError,
         }
         with map_exceptions(exc_map):
             with anyio.fail_after(timeout):
@@ -43,6 +44,7 @@ class AsyncIOStream(AsyncNetworkStream):
         exc_map = {
             TimeoutError: WriteTimeout,
             anyio.BrokenResourceError: WriteError,
+            anyio.ClosedResourceError: WriteError,
         }
         with map_exceptions(exc_map):
             with anyio.fail_after(timeout):
diff --git a/httpcore/backends/mock.py b/httpcore/backends/mock.py
index 8491f6d..9aba0ea 100644
--- a/httpcore/backends/mock.py
+++ b/httpcore/backends/mock.py
@@ -2,6 +2,7 @@ import ssl
 import typing
 from typing import Optional
 
+from .._exceptions import ReadError
 from .base import AsyncNetworkBackend, AsyncNetworkStream, NetworkBackend, NetworkStream
 
 
@@ -17,8 +18,11 @@ class MockStream(NetworkStream):
     def __init__(self, buffer: typing.List[bytes], http2: bool = False) -> None:
         self._buffer = buffer
         self._http2 = http2
+        self._closed = False
 
     def read(self, max_bytes: int, timeout: Optional[float] = None) -> bytes:
+        if self._closed:
+            raise ReadError("Connection closed")
         if not self._buffer:
             return b""
         return self._buffer.pop(0)
@@ -27,7 +31,7 @@ class MockStream(NetworkStream):
         pass
 
     def close(self) -> None:
-        pass
+        self._closed = True
 
     def start_tls(
         self,
@@ -68,8 +72,11 @@ class AsyncMockStream(AsyncNetworkStream):
     def __init__(self, buffer: typing.List[bytes], http2: bool = False) -> None:
         self._buffer = buffer
         self._http2 = http2
+        self._closed = False
 
     async def read(self, max_bytes: int, timeout: Optional[float] = None) -> bytes:
+        if self._closed:
+            raise ReadError("Connection closed")
         if not self._buffer:
             return b""
         return self._buffer.pop(0)
@@ -78,7 +85,7 @@ class AsyncMockStream(AsyncNetworkStream):
         pass
 
     async def aclose(self) -> None:
-        pass
+        self._closed = True
 
     async def start_tls(
         self,
diff --git a/httpcore/backends/trio.py b/httpcore/backends/trio.py
index 7786d02..951016c 100644
--- a/httpcore/backends/trio.py
+++ b/httpcore/backends/trio.py
@@ -27,6 +27,7 @@ class TrioStream(AsyncNetworkStream):
         exc_map: ExceptionMapping = {
             trio.TooSlowError: ReadTimeout,
             trio.BrokenResourceError: ReadError,
+            trio.ClosedResourceError: ReadError,
         }
         with map_exceptions(exc_map):
             with trio.fail_after(timeout_or_inf):
@@ -43,6 +44,7 @@ class TrioStream(AsyncNetworkStream):
         exc_map: ExceptionMapping = {
             trio.TooSlowError: WriteTimeout,
             trio.BrokenResourceError: WriteError,
+            trio.ClosedResourceError: WriteError,
         }
         with map_exceptions(exc_map):
             with trio.fail_after(timeout_or_inf):

diff --git a/tests/_async/test_connection_pool.py b/tests/_async/test_connection_pool.py
index 684e9ba..d2ac58a 100644
--- a/tests/_async/test_connection_pool.py
+++ b/tests/_async/test_connection_pool.py
@@ -3,7 +3,13 @@ from typing import List, Optional
 import pytest
 import trio as concurrency
 
-from httpcore import AsyncConnectionPool, ConnectError, PoolTimeout, UnsupportedProtocol
+from httpcore import (
+    AsyncConnectionPool,
+    ConnectError,
+    PoolTimeout,
+    ReadError,
+    UnsupportedProtocol,
+)
 from httpcore.backends.base import AsyncNetworkStream
 from httpcore.backends.mock import AsyncMockBackend
 
@@ -463,9 +469,10 @@ async def test_connection_pool_closed_while_request_in_flight():
     ) as pool:
         # Send a request, and then close the connection pool while the
         # response has not yet been streamed.
-        async with pool.stream("GET", "https://example.com/"):
-            with pytest.raises(RuntimeError):
-                await pool.aclose()
+        async with pool.stream("GET", "https://example.com/") as response:
+            await pool.aclose()
+            with pytest.raises(ReadError):
+                await response.aread()
 
 
 @pytest.mark.anyio
diff --git a/tests/_sync/test_connection_pool.py b/tests/_sync/test_connection_pool.py
index 3ab0c87..453b7fd 100644
--- a/tests/_sync/test_connection_pool.py
+++ b/tests/_sync/test_connection_pool.py
@@ -3,7 +3,13 @@ from typing import List, Optional
 import pytest
 from tests import concurrency
 
-from httpcore import ConnectionPool, ConnectError, PoolTimeout, UnsupportedProtocol
+from httpcore import (
+    ConnectionPool,
+    ConnectError,
+    PoolTimeout,
+    ReadError,
+    UnsupportedProtocol,
+)
 from httpcore.backends.base import NetworkStream
 from httpcore.backends.mock import MockBackend
 
@@ -463,9 +469,10 @@ def test_connection_pool_closed_while_request_in_flight():
     ) as pool:
         # Send a request, and then close the connection pool while the
         # response has not yet been streamed.
-        with pool.stream("GET", "https://example.com/"):
-            with pytest.raises(RuntimeError):
-                pool.close()
+        with pool.stream("GET", "https://example.com/") as response:
+            pool.close()
+            with pytest.raises(ReadError):
+                response.read()
 
 
 

List in-flight connections
`AsyncConnectionPool.aclose()` raises `RuntimeError: The connection pool was closed while 1 HTTP requests/responses were still in-flight.` if there are any on-going requests.

It would be nice to provide a list of URLs to help me understand what I'm doing wrong. At the moment I'm adding `print` statements to the httpcore code to figure this out.

Something like this would be nice:

```
RuntimeError: The connection pool was closed while 3 HTTP requests/responses were still in-flight:
URL(scheme=b'https', host=b'www.example.com', port=None, target=b'/foo')
URL(scheme=b'https', host=b'www.example.com', port=None, target=b'/bar')
URL(scheme=b'https', host=b'www.example.net', port=None, target=b'/baz')
```

tests/_async/test_connection_pool.py::test_connection_pool_closed_while_request_in_flight[asyncio] tests/_async/test_connection_pool.py::test_connection_pool_closed_while_request_in_flight[trio] tests/_sync/test_connection_pool.py::test_connection_pool_closed_while_request_in_flight
tests/_async/test_connection_pool.py::test_connection_pool_with_keepalive[asyncio] tests/_async/test_connection_pool.py::test_connection_pool_with_close[asyncio] tests/_async/test_connection_pool.py::test_trace_request[asyncio] tests/_async/test_connection_pool.py::test_connection_pool_with_http_exception[asyncio] tests/_async/test_connection_pool.py::test_connection_pool_with_connect_exception[asyncio] tests/_async/test_connection_pool.py::test_connection_pool_with_immediate_expiry[asyncio] tests/_async/test_connection_pool.py::test_connection_pool_with_no_keepalive_connections_allowed[asyncio] tests/_async/test_connection_pool.py::test_unsupported_protocol[asyncio] tests/_async/test_connection_pool.py::test_connection_pool_timeout[asyncio] tests/_async/test_connection_pool.py::test_http11_upgrade_connection[asyncio] tests/_async/test_connection_pool.py::test_connection_pool_with_keepalive[trio] tests/_async/test_connection_pool.py::test_connection_pool_with_close[trio] tests/_async/test_connection_pool.py::test_trace_request[trio] tests/_async/test_connection_pool.py::test_connection_pool_with_http_exception[trio] tests/_async/test_connection_pool.py::test_connection_pool_with_connect_exception[trio] tests/_async/test_connection_pool.py::test_connection_pool_with_immediate_expiry[trio] tests/_async/test_connection_pool.py::test_connection_pool_with_no_keepalive_connections_allowed[trio] tests/_async/test_connection_pool.py::test_unsupported_protocol[trio] tests/_async/test_connection_pool.py::test_connection_pool_timeout[trio] tests/_async/test_connection_pool.py::test_http11_upgrade_connection[trio] tests/_async/test_connection_pool.py::test_connection_pool_concurrency tests/_async/test_connection_pool.py::test_connection_pool_concurrency_same_domain_closing tests/_async/test_connection_pool.py::test_connection_pool_concurrency_same_domain_keepalive tests/_sync/test_connection_pool.py::test_connection_pool_with_keepalive tests/_sync/test_connection_pool.py::test_connection_pool_with_close tests/_sync/test_connection_pool.py::test_trace_request tests/_sync/test_connection_pool.py::test_connection_pool_with_http_exception tests/_sync/test_connection_pool.py::test_connection_pool_with_connect_exception tests/_sync/test_connection_pool.py::test_connection_pool_with_immediate_expiry tests/_sync/test_connection_pool.py::test_connection_pool_with_no_keepalive_connections_allowed tests/_sync/test_connection_pool.py::test_connection_pool_concurrency tests/_sync/test_connection_pool.py::test_connection_pool_concurrency_same_domain_closing tests/_sync/test_connection_pool.py::test_connection_pool_concurrency_same_domain_keepalive tests/_sync/test_connection_pool.py::test_unsupported_protocol tests/_sync/test_connection_pool.py::test_connection_pool_timeout tests/_sync/test_connection_pool.py::test_http11_upgrade_connection