diff --git a/src/quant_platform_kit/longbridge/execution.py b/src/quant_platform_kit/longbridge/execution.py
index 136939d..b4bf38b 100644
--- a/src/quant_platform_kit/longbridge/execution.py
+++ b/src/quant_platform_kit/longbridge/execution.py
@@ -40,7 +40,7 @@ def submit_order(
     order_type = OrderType.LO if order_kind == "limit" else OrderType.MO
     order_side = OrderSide.Buy if side == "buy" else OrderSide.Sell
     submitted_quantity = Decimal(str(quantity))
-    if submitted_quantity < Decimal("1") or submitted_quantity != submitted_quantity.to_integral_value():
+    if submitted_quantity < Decimal("1"):
         return ExecutionReport(
             symbol=symbol.split(".")[0],
             side=side,
@@ -48,8 +48,21 @@ def submit_order(
             status="rejected",
             raw_payload={
                 "detail": (
-                    "LongBridge submitted_quantity must be a whole-share quantity "
-                    "of at least 1 share; "
+                    "LongBridge submitted_quantity must be at least 1 share; "
+                    f"got {submitted_quantity}."
+                ),
+                "order_kind": order_kind,
+            },
+        )
+    if side == "buy" and submitted_quantity != submitted_quantity.to_integral_value():
+        return ExecutionReport(
+            symbol=symbol.split(".")[0],
+            side=side,
+            quantity=float(quantity),
+            status="rejected",
+            raw_payload={
+                "detail": (
+                    "LongBridge fractional buy orders are not supported by this adapter; "
                     f"got {submitted_quantity}."
                 ),
                 "order_kind": order_kind,
diff --git a/tests/test_longbridge_execution.py b/tests/test_longbridge_execution.py
index 65f017b..cc71b92 100644
--- a/tests/test_longbridge_execution.py
+++ b/tests/test_longbridge_execution.py
@@ -102,10 +102,10 @@ def test_submit_order_rejects_quantity_below_one_before_api_call(self) -> None:
             )
 
         self.assertEqual(report.status, "rejected")
-        self.assertIn("whole-share quantity of at least 1 share", report.raw_payload["detail"])
+        self.assertIn("at least 1 share", report.raw_payload["detail"])
         self.assertFalse(hasattr(ctx, "submit_args"))
 
-    def test_submit_order_rejects_fractional_quantity_before_api_call(self) -> None:
+    def test_submit_order_rejects_fractional_buy_before_api_call(self) -> None:
         longport_module = types.ModuleType("longport")
         openapi_module = types.ModuleType("longport.openapi")
         openapi_module.OrderSide = types.SimpleNamespace(Buy="Buy", Sell="Sell")
@@ -124,9 +124,23 @@ def test_submit_order_rejects_fractional_quantity_before_api_call(self) -> None:
             )
 
         self.assertEqual(report.status, "rejected")
-        self.assertIn("whole-share quantity of at least 1 share", report.raw_payload["detail"])
+        self.assertIn("fractional buy orders are not supported", report.raw_payload["detail"])
         self.assertFalse(hasattr(ctx, "submit_args"))
 
+    def test_submit_order_allows_fractional_sell_at_or_above_one_share(self) -> None:
+        longport_module = types.ModuleType("longport")
+        openapi_module = types.ModuleType("longport.openapi")
+        openapi_module.OrderSide = types.SimpleNamespace(Buy="Buy", Sell="Sell")
+        openapi_module.OrderType = types.SimpleNamespace(LO="LO", MO="MO")
+        openapi_module.TimeInForceType = types.SimpleNamespace(Day="Day")
+
+        ctx = FakeTradeContext()
+        with patch.dict(sys.modules, {"longport": longport_module, "longport.openapi": openapi_module}):
+            report = submit_order(ctx, "BOXX.US", order_kind="market", side="sell", quantity=4.6177)
+
+        self.assertEqual(report.status, "submitted")
+        self.assertEqual(str(ctx.submit_args[3]), "4.6177")
+
     def test_fetch_order_status(self) -> None:
         status = fetch_order_status(FakeTradeContext(), "OID-1")