diff git a/nifty5/operators/energy_operators.py b/nifty5/operators/energy_operators.py
index 91a23db8fbe5710ff2df8b78aaaea33ef54bd8ea..70f79de170baa88c79e2831269ccf55a55061a43 100644
 a/nifty5/operators/energy_operators.py
+++ b/nifty5/operators/energy_operators.py
@@ 122,9 +122,8 @@ class GaussianEnergy(EnergyOperator):
"""
def __init__(self, mean=None, covariance=None, domain=None):
 if mean is not None and not isinstance(mean, Field):
 if not isinstance(mean, MultiField):
 raise TypeError
+ if mean is not None and not isinstance(mean, (Field, MultiField)):
+ raise TypeError
if covariance is not None and not isinstance(covariance,
LinearOperator):
raise TypeError
@@ 309,7 +308,6 @@ class StandardHamiltonian(EnergyOperator):
Tells an internal :class:`SamplingEnabler` which convergence criterion
to use to draw Gaussian samples.

See also

`Encoding prior knowledge in the structure of the likelihood`,