diff --git a/httpcore/_models.py b/httpcore/_models.py
index 8a65f1334..d63ba4ee4 100644
--- a/httpcore/_models.py
+++ b/httpcore/_models.py
@@ -275,6 +275,10 @@ def __init__(
         else:
             self.scheme = enforce_bytes(scheme, name="scheme")
             self.host = enforce_bytes(host, name="host")
+            # bool is a subclass of int; reject it so port=True does not become 1.
+            if port is not None and (isinstance(port, bool) or not isinstance(port, int)):
+                seen = type(port).__name__
+                raise TypeError(f"port must be int or None, but got {seen}.")
             self.port = port
             self.target = enforce_bytes(target, name="target")
 
diff --git a/tests/test_models.py b/tests/test_models.py
index 7dd6e419d..d63f55445 100644
--- a/tests/test_models.py
+++ b/tests/test_models.py
@@ -187,3 +187,19 @@ async def test_response_async_streaming():
     with pytest.raises(RuntimeError):
         async for chunk in response.aiter_stream():
             pass  # pragma: nocover
+
+
+def test_url_rejects_bool_port():
+    # isinstance(True, int) is True; without an explicit check, port=True
+    # becomes port 1 in bytes(url) ("http://host:1/").
+    with pytest.raises(TypeError, match="port must be int or None"):
+        httpcore.URL(scheme=b"http", host=b"www.example.com", port=True, target=b"/")
+    with pytest.raises(TypeError, match="port must be int or None"):
+        httpcore.URL(scheme=b"http", host=b"www.example.com", port=False, target=b"/")
+
+
+def test_url_rejects_non_int_port():
+    with pytest.raises(TypeError, match="port must be int or None"):
+        httpcore.URL(scheme=b"http", host=b"www.example.com", port=1.5, target=b"/")  # type: ignore
+    with pytest.raises(TypeError, match="port must be int or None"):
+        httpcore.URL(scheme=b"http", host=b"www.example.com", port="80", target=b"/")  # type: ignore