diff --git a/GPy/kern/src/symmetric.py b/GPy/kern/src/symmetric.py
index c7207023..8797a5a3 100644
--- a/GPy/kern/src/symmetric.py
+++ b/GPy/kern/src/symmetric.py
@@ -168,3 +168,8 @@ class Symmetric(Kern):
                 + self.base_kernel.gradients_X(dL_dK, X_sym, X2_sym).dot(self.transform.T)
                 + self.symmetry_sign * self.base_kernel.gradients_X(dL_dK, X, X2_sym)
                 + self.symmetry_sign * self.base_kernel.gradients_X(dL_dK, X_sym, X2).dot(self.transform.T))
+
+def gradients_X_diag(self, dL_dKdiag, X):
+    X_sym = X.dot(self.transform)
+    return ((1 + self.symmetry_sign) * (self.base_kernel.gradients_X_diag(dL_dKdiag, X)
+                                        + self.base_kernel.gradients_X_diag(dL_dKdiag, X_sym).dot(self.transform.T)))