diff --git a/backend/app/main.py b/backend/app/main.py
index ae5788af..5dd3f06a 100644
--- a/backend/app/main.py
+++ b/backend/app/main.py
@@ -132,7 +132,7 @@ async def lifespan(_: FastAPI) -> AsyncIterator[None]:
     # actually need cookie-based auth.
     allow_credentials=False,
     # Explicit allowlist (avoid "*") so CORS behavior is reviewable.
-    allow_methods=["GET", "POST", "OPTIONS"],
+    allow_methods=["GET", "POST", "PUT", "DELETE", "OPTIONS"],
     allow_headers=CORS_ALLOW_HEADERS,
 )
 
diff --git a/backend/tests/test_cors_methods.py b/backend/tests/test_cors_methods.py
new file mode 100644
index 00000000..645e4232
--- /dev/null
+++ b/backend/tests/test_cors_methods.py
@@ -0,0 +1,53 @@
+from __future__ import annotations
+
+from fastapi.testclient import TestClient
+
+from app.main import app
+
+
+API_CORS_METHODS = ("GET", "POST", "PUT", "DELETE", "OPTIONS")
+UNSUPPORTED_API_CORS_METHOD = "PATCH"
+
+
+def test_cors_preflight_allows_every_supported_api_method() -> None:
+    """Production CORS preflight must accept every HTTP method exposed by the API."""
+
+    client = TestClient(app)
+
+    for method in API_CORS_METHODS:
+        response = client.options(
+            "/api/projects",
+            headers={
+                "Origin": "http://localhost:5173",
+                "Access-Control-Request-Method": method,
+                "Access-Control-Request-Headers": "Content-Type",
+            },
+        )
+
+        assert response.status_code in (200, 204)
+        allowed_methods = {
+            item.strip()
+            for item in response.headers["Access-Control-Allow-Methods"].split(",")
+        }
+        assert method in allowed_methods
+
+
+def test_cors_preflight_rejects_unexposed_api_method() -> None:
+    """Production CORS must reject methods that have no registered API route."""
+
+    client = TestClient(app)
+    response = client.options(
+        "/api/projects",
+        headers={
+            "Origin": "http://localhost:5173",
+            "Access-Control-Request-Method": UNSUPPORTED_API_CORS_METHOD,
+            "Access-Control-Request-Headers": "Content-Type",
+        },
+    )
+
+    assert response.status_code == 400
+    allowed_methods = {
+        item.strip()
+        for item in response.headers["Access-Control-Allow-Methods"].split(",")
+    }
+    assert UNSUPPORTED_API_CORS_METHOD not in allowed_methods