diff --git a/wfl/cli/cli_options.py b/wfl/cli/cli_options.py
index fd0bc65b..1df7c414 100644
--- a/wfl/cli/cli_options.py
+++ b/wfl/cli/cli_options.py
@@ -1,4 +1,5 @@
 import click
+import json
 from wfl.configset import ConfigSet, OutputSpec
 from ase.io.extxyz import key_val_str_to_dict
 
@@ -38,6 +39,16 @@ def param_fname(f):
     f = click.option("--param-fname", "-pf", type=click.Path(), help="Path to the potential parameter file")(f)
     return f
 
+def _parse_kwargs(ctx, param, value):
+    if value is not None:
+        return json.loads(value)
+    else:
+        return {}
+
+def kwargs(f):
+    f = click.option("--kwargs", "-kw", callback=_parse_kwargs, help="JSON text with additional Calculator constructor kwargs")(f)
+    return f
+
 def prop_prefix(f):
     f = click.option("--prop-prefix", "-pp", help='Prefix to be pre-pended to all evaluate properties. '
                                                   'Defaults to "gap_"/"ace_"/"mace_" as appropriate')(f)
diff --git a/wfl/cli/commands/eval.py b/wfl/cli/commands/eval.py
index b4d2c4b3..8d04d778 100644
--- a/wfl/cli/commands/eval.py
+++ b/wfl/cli/commands/eval.py
@@ -16,9 +16,10 @@ def pyjulip_ace(param_fname):
 @opt.inputs
 @opt.outputs
 @opt.param_fname
+@opt.kwargs
 @opt.prop_prefix
 @opt.num_inputs_per_python_subprocess
-def gap(ctx, inputs, outputs, param_fname, prop_prefix, num_inputs_per_python_subprocess):
+def gap(ctx, inputs, outputs, param_fname, kwargs, prop_prefix, num_inputs_per_python_subprocess):
     """evaluates GAP"""
 
     from quippy.potential import Potential
@@ -26,7 +27,9 @@ def gap(ctx, inputs, outputs, param_fname, prop_prefix, num_inputs_per_python_su
     if prop_prefix is None:
         prop_prefix = "gap_"
 
-    calc = (Potential, [], {"param_filename": param_fname})
+    kwargs_use = {"param_filename": param_fname}
+    kwargs_use.update(kwargs)
+    calc = (Potential, [], kwargs_use)
 
     generic.calculate(
         inputs=inputs,
@@ -41,15 +44,16 @@ def gap(ctx, inputs, outputs, param_fname, prop_prefix, num_inputs_per_python_su
 @opt.inputs
 @opt.outputs
 @opt.param_fname
+@opt.kwargs
 @opt.prop_prefix
 @opt.num_inputs_per_python_subprocess
-def ace(ctx, inputs, outputs, param_fname, prop_prefix, num_inputs_per_python_subprocess):
+def ace(ctx, inputs, outputs, param_fname, kwargs, prop_prefix, num_inputs_per_python_subprocess):
     """evaluates ACE"""
 
     if prop_prefix is None:
         prop_prefix = 'ace_'
 
-    calc = (pyjulip_ace, [param_fname], {})
+    calc = (pyjulip_ace, [param_fname], kwargs)
 
     generic.calculate(
         inputs=inputs,
@@ -64,9 +68,10 @@ def ace(ctx, inputs, outputs, param_fname, prop_prefix, num_inputs_per_python_su
 @opt.inputs
 @opt.outputs
 @opt.param_fname
+@opt.kwargs
 @opt.prop_prefix
 @opt.num_inputs_per_python_subprocess
-def mace(ctx, inputs, outputs, param_fname, prop_prefix, num_inputs_per_python_subprocess):
+def mace(ctx, inputs, outputs, param_fname, kwargs, prop_prefix, num_inputs_per_python_subprocess):
     """evaluates MACE"""
 
     from mace.calculators import MACECalculator
@@ -74,7 +79,9 @@ def mace(ctx, inputs, outputs, param_fname, prop_prefix, num_inputs_per_python_s
     if prop_prefix is None:
         prop_prefix = 'mace_'
 
-    calc = (MACECalculator, [], {"model_paths": param_fname, "device": "cpu"})
+    kwargs_use = {"model_paths": param_fname, "device": "cpu"}
+    kwargs_use.update(kwargs)
+    calc = (MACECalculator, [], kwargs_use)
 
     generic.calculate(
         inputs=inputs,
diff --git a/wfl/generate/optimize.py b/wfl/generate/optimize.py
index 43694326..a3443bdb 100644
--- a/wfl/generate/optimize.py
+++ b/wfl/generate/optimize.py
@@ -93,7 +93,11 @@ def _run_autopara_wrappable(atoms, calculator, fmax=1.0e-3, smax=None, steps=100
 
     if keep_symmetry:
         # noinspection PyUnresolvedReferences,PyUnresolvedReferences
-        from ase.spacegroup.symmetrize import FixSymmetry
+        try:
+            from ase.constraints import FixSymmetry
+        except ImportError:
+            # fall back to previous import location (pre MR 3288)
+            from ase.spacegroup.symmetrize import FixSymmetry
 
     all_trajs = []