diff --git a/src/connector/C#/src/TDengineDriver/TDengineDriver.cs b/src/connector/C#/src/TDengineDriver/TDengineDriver.cs
index 411740635516f25682bd27adf5013eb84bc61fa3..8b53bda5622945f2dfb27dc5426ab96e9dbe9be5 100644
--- a/src/connector/C#/src/TDengineDriver/TDengineDriver.cs
+++ b/src/connector/C#/src/TDengineDriver/TDengineDriver.cs
@@ -277,7 +277,7 @@ namespace TDengineDriver
         static extern public IntPtr FetchRows(IntPtr res);
 
         [DllImport("taos", EntryPoint = "taos_free_result", CallingConvention = CallingConvention.Cdecl)]
-        static extern public IntPtr FreeResult(IntPtr res);
+        static extern public void FreeResult(IntPtr res);
 
         [DllImport("taos", EntryPoint = "taos_close", CallingConvention = CallingConvention.Cdecl)]
         static extern public void Close(IntPtr taos);