diff --git a/fasthtml/core.py b/fasthtml/core.py
index 58c00f4c..449415b8 100644
--- a/fasthtml/core.py
+++ b/fasthtml/core.py
@@ -742,12 +742,19 @@ def __repr__(self) -> str:
 # %% ../nbs/api/00_core.ipynb #e0accf76
 @patch
 def add_route(self:FastHTML, route):
-    "Add or replace a route in the FastHTML app"
+    "Add or replace a route, rejecting ambiguous method overlaps on the same path and host"
     route.methods = [m.upper() for m in listify(route.methods)]
-    self.router.routes = [r for r in self.router.routes if not
-        (r.path==route.path and r.name == route.name and
-            ((route.methods is None) or (set(r.methods) == set(route.methods))))]
-    self.router.routes.append(route)
+    meths = set(route.methods)
+    routes = []
+    for r in self.router.routes:
+        if (r.path==route.path and r.name == route.name and
+            ((route.methods is None) or (set(r.methods or ()) == meths))): continue
+        overlap = set(r.methods or ()) & meths
+        if (r.path == route.path and getattr(r, 'host', None) == getattr(route, 'host', None)
+            and overlap):
+            raise ValueError(f"Overlapping route methods {sorted(overlap)!r} for path {route.path!r}")
+        routes.append(r)
+    self.router.routes = routes + [route]
     self.router.routes.sort(key=lambda r: not getattr(r, 'host', None))
 
 
diff --git a/nbs/api/00_core.ipynb b/nbs/api/00_core.ipynb
index 9238c3a0..050467b3 100644
--- a/nbs/api/00_core.ipynb
+++ b/nbs/api/00_core.ipynb
@@ -2108,12 +2108,19 @@
     "#| export\n",
     "@patch\n",
     "def add_route(self:FastHTML, route):\n",
-    "    \"Add or replace a route in the FastHTML app\"\n",
+    "    \"Add or replace a route, rejecting ambiguous method overlaps on the same path and host\"\n",
     "    route.methods = [m.upper() for m in listify(route.methods)]\n",
-    "    self.router.routes = [r for r in self.router.routes if not\n",
-    "        (r.path==route.path and r.name == route.name and\n",
-    "            ((route.methods is None) or (set(r.methods) == set(route.methods))))]\n",
-    "    self.router.routes.append(route)\n",
+    "    meths = set(route.methods)\n",
+    "    routes = []\n",
+    "    for r in self.router.routes:\n",
+    "        if (r.path==route.path and r.name == route.name and\n",
+    "            ((route.methods is None) or (set(r.methods or ()) == meths))): continue\n",
+    "        overlap = set(r.methods or ()) & meths\n",
+    "        if (r.path == route.path and getattr(r, 'host', None) == getattr(route, 'host', None)\n",
+    "            and overlap):\n",
+    "            raise ValueError(f\"Overlapping route methods {sorted(overlap)!r} for path {route.path!r}\")\n",
+    "        routes.append(r)\n",
+    "    self.router.routes = routes + [route]\n",
     "    self.router.routes.sort(key=lambda r: not getattr(r, 'host', None))\n"
    ]
   },
diff --git a/tests/test_routing.py b/tests/test_routing.py
new file mode 100644
index 00000000..8f1b21d6
--- /dev/null
+++ b/tests/test_routing.py
@@ -0,0 +1,34 @@
+import pytest
+
+from fasthtml.core import FastHTML
+
+
+def _app():
+    return FastHTML(secret_key="synthetic-test-only", sess_cls=None)
+
+
+def test_default_route_rejects_overlapping_sibling_method():
+    app = _app()
+    app.route("/shared")(lambda req: "default")
+
+    with pytest.raises(ValueError, match="POST"):
+        app.post("/shared")(lambda req: "post")
+
+
+def test_explicit_disjoint_methods_can_share_path():
+    app = _app()
+    app.get("/shared", name="shared_get")(lambda req: "get")
+    app.post("/shared", name="shared_post")(lambda req: "post")
+
+    assert [route.name for route in app.router.routes if route.path == "/shared"] == [
+        "shared_get",
+        "shared_post",
+    ]
+
+
+def test_same_name_and_methods_replace_existing_route():
+    app = _app()
+    app.get("/shared", name="shared")(lambda req: "first")
+    app.get("/shared", name="shared")(lambda req: "replacement")
+
+    assert len([route for route in app.router.routes if route.path == "/shared"]) == 1