diff --git a/fastapi/openapi/utils.py b/fastapi/openapi/utils.py
index 812003aee3..c7c92350cc 100644
--- a/fastapi/openapi/utils.py
+++ b/fastapi/openapi/utils.py
@@ -242,7 +242,14 @@ def get_openapi_operation_metadata(
     operation["summary"] = generate_operation_summary(route=route, method=method)
     if route.description:
         operation["description"] = route.description
-    operation_id = route.operation_id or route.unique_id
+    if route.operation_id:
+        operation_id = route.operation_id
+    elif route.methods is not None and len(route.methods) > 1:
+        # When a route handles multiple HTTP methods, append the current
+        # method to create unique operation IDs per method
+        operation_id = f"{route.unique_id}_{method.lower()}"
+    else:
+        operation_id = route.unique_id
     if operation_id in operation_ids:
         message = (
             f"Duplicate Operation ID {operation_id} for function "
diff --git a/tests/test_duplicate_operation_id_multiple_methods.py b/tests/test_duplicate_operation_id_multiple_methods.py
new file mode 100644
index 0000000000..53b103759d
--- /dev/null
+++ b/tests/test_duplicate_operation_id_multiple_methods.py
@@ -0,0 +1,71 @@
+import warnings
+
+from fastapi import FastAPI
+from fastapi.testclient import TestClient
+
+
+def test_no_duplicate_operation_id_with_multiple_methods():
+    """Ensure routes with multiple methods get unique operation IDs."""
+    with warnings.catch_warnings(record=True) as w:
+        warnings.simplefilter("always")
+
+        app = FastAPI()
+
+        def handler():
+            return {"status": "ok"}  # pragma: nocover
+
+        app.add_api_route("/items", handler, methods=["POST", "DELETE"])
+
+        client = TestClient(app)
+        response = client.get("/openapi.json")
+        assert response.status_code == 200
+        schema = response.json()
+
+        post_op = schema["paths"]["/items"]["post"]
+        delete_op = schema["paths"]["/items"]["delete"]
+
+        assert post_op["operationId"] != delete_op["operationId"]
+        assert "post" in post_op["operationId"]
+        assert "delete" in delete_op["operationId"]
+
+        dup_warnings = [x for x in w if "Duplicate" in str(x.message)]
+        assert len(dup_warnings) == 0
+
+
+def test_single_method_route_operation_id_unchanged():
+    """Ensure single-method routes still generate the same operation IDs."""
+    app = FastAPI()
+
+    @app.get("/items")
+    def get_items():
+        return []  # pragma: nocover
+
+    client = TestClient(app)
+    response = client.get("/openapi.json")
+    schema = response.json()
+
+    get_op = schema["paths"]["/items"]["get"]
+    assert get_op["operationId"] == "get_items_items_get"
+
+
+def test_three_methods_unique_operation_ids():
+    """Ensure routes with three methods all get unique operation IDs."""
+    app = FastAPI()
+
+    def handler():
+        return {"status": "ok"}  # pragma: nocover
+
+    app.add_api_route("/items", handler, methods=["GET", "POST", "DELETE"])
+
+    client = TestClient(app)
+    response = client.get("/openapi.json")
+    schema = response.json()
+
+    get_op = schema["paths"]["/items"]["get"]
+    post_op = schema["paths"]["/items"]["post"]
+    delete_op = schema["paths"]["/items"]["delete"]
+
+    assert "get" in get_op["operationId"]
+    assert "post" in post_op["operationId"]
+    assert "delete" in delete_op["operationId"]
+    assert len({get_op["operationId"], post_op["operationId"], delete_op["operationId"]}) == 3