diff --git a/src/TensorFlowNET.Core/Gradients/math_grad.cs b/src/TensorFlowNET.Core/Gradients/math_grad.cs
index 672270b9..85f849cc 100644
--- a/src/TensorFlowNET.Core/Gradients/math_grad.cs
+++ b/src/TensorFlowNET.Core/Gradients/math_grad.cs
@@ -96,6 +96,13 @@ namespace Tensorflow.Gradients
             });
         }
 
+        [RegisterGradient("GreaterEqual")]
+        public static Tensor[] _GreaterEqualGrad(Operation op, Tensor[] grads)
+        {
+            var grad = grads[0];
+            throw new NotImplementedException("_GreaterEqualGrad");
+        }
+
         [RegisterGradient("Identity")]
         public static Tensor[] _IdGrad(Operation op, Tensor[] grads)
         {
@@ -124,6 +131,17 @@ namespace Tensorflow.Gradients
             });
         }
 
+        [RegisterGradient("Log1p")]
+        public static Tensor[] _Log1pGrad(Operation op, Tensor[] grads)
+        {
+            var grad = grads[0];
+            var x = op.inputs[0];
+            return tf_with(ops.control_dependencies(new Operation[] { grad }), dp => {
+                x = math_ops.conj(x);
+                return new Tensor[] { grad * math_ops.reciprocal(1 + x) };
+            });
+        }
+
         [RegisterGradient("Mul")]
         public static Tensor[] _MulGrad(Operation op, Tensor[] grads)
         {
@@ -332,6 +350,21 @@ namespace Tensorflow.Gradients
             return new Tensor[] { -grads[0] };
         }
 
+        [RegisterGradient("Select")]
+        public static Tensor[] _SelectGrad(Operation op, Tensor[] grads)
+        {
+            var grad = grads[0];
+            var c = op.inputs[0];
+            var x = op.inputs[1];
+            var zeros = array_ops.zeros_like(x);
+            return new Tensor[]
+            {
+                null,
+                array_ops.where(c, grad, zeros),
+                array_ops.where(c, zeros, grad)
+            };
+        }
+
         private static Tensor _safe_shape_div(Tensor x, Tensor y)
         {
             return math_ops.floordiv(x, gen_math_ops.maximum(y, 1));
@@ -363,7 +396,7 @@ namespace Tensorflow.Gradients
             var grad_shape = grad._shape_tuple();
             return Enumerable.SequenceEqual(x_shape, y_shape) &&
                 Enumerable.SequenceEqual(y_shape, grad_shape) &&
-                x.NDims != -1 &&
+                x_shape.Length > -1 &&
                 !x_shape.Contains(-1);
         }