diff --git a/ffi/cs/mcl/mcl.cs b/ffi/cs/mcl/mcl.cs
index 17d69f83..9f311095 100644
--- a/ffi/cs/mcl/mcl.cs
+++ b/ffi/cs/mcl/mcl.cs
@@ -91,6 +91,7 @@ public class MCL {
 
         [DllImport(dllName)] public static extern void mclBnGT_clear(ref GT x);
         [DllImport(dllName)] public static extern int mclBnGT_setStr(ref GT x, [In][MarshalAs(UnmanagedType.LPStr)] string buf, long bufSize, int ioMode);
+        [DllImport(dllName)] public static extern int mclBnGT_isValid(in GT x);
         [DllImport(dllName)] public static extern int mclBnGT_isEqual(in GT x, in GT y);
         [DllImport(dllName)] public static extern int mclBnGT_isZero(in GT x);
         [DllImport(dllName)] public static extern int mclBnGT_isOne(in GT x);
@@ -929,6 +930,10 @@ public void SetStr(String s, int ioMode)
                     throw new ArgumentException("mclBnGT_setStr:" + s);
                 }
             }
+            public bool IsValid()
+            {
+                return mclBnGT_isValid(this) == 1;
+            }
             public bool Equals(in GT rhs)
             {
                 return mclBnGT_isEqual(this, rhs) == 1;