diff --git a/Modules/Cluster.py b/Modules/Cluster.py
index 0664914b..fe2a7f99 100644
--- a/Modules/Cluster.py
+++ b/Modules/Cluster.py
@@ -333,6 +333,30 @@ def __setattr__(self, name, value):
             super(Cluster, self).__setattr__(name, value)
 
 
+    def __getstate__(self):
+        """
+        Return the picklable state of the cluster.
+
+        The thread lock created by compute_ensemble_batch cannot be pickled,
+        so it is dropped here. This allows sscha.Utilities.save_binary to
+        store objects holding a cluster after a calculation has run.
+        """
+        state = self.__dict__.copy()
+        state["lock"] = None
+        return state
+
+
+    def __setstate__(self, state):
+        """
+        Restore the cluster from a pickled state.
+
+        The thread lock is transient runtime state and is reset to None,
+        as after __init__; compute_ensemble_batch recreates it when needed.
+        """
+        state["lock"] = None
+        self.__dict__.update(state)
+
+
 
     def copy_file(self, source, destination, server_source = False, server_dest = True, raise_error=False, **kwargs):
         """
diff --git a/tests/test_save_binary/test_save_binary.py b/tests/test_save_binary/test_save_binary.py
new file mode 100644
index 00000000..cf777bc7
--- /dev/null
+++ b/tests/test_save_binary/test_save_binary.py
@@ -0,0 +1,65 @@
+# -*- coding: utf-8 -*-
+from __future__ import print_function
+from __future__ import division
+
+import os
+import tempfile
+import threading
+
+import cellconstructor as CC
+import cellconstructor.Phonons
+
+import sscha
+import sscha.Cluster
+import sscha.Ensemble
+import sscha.Relax
+import sscha.SchaMinimizer
+import sscha.Utilities
+
+"""
+Regression test for issue #114: save_binary failed with
+TypeError: cannot pickle '_thread.lock' object
+when the relax object holds a cluster that already ran a calculation
+(Cluster.compute_ensemble_batch stores a threading.Lock on the cluster).
+"""
+
+
+def test_save_binary_relax_with_cluster(verbose=False):
+    total_path = os.path.dirname(os.path.abspath(__file__))
+    os.chdir(total_path)
+
+    DATA_PATH = "../../Examples/ensemble_data_test/"
+
+    dyn = CC.Phonons.Phonons(os.path.join(DATA_PATH, "dyn"))
+
+    ens = sscha.Ensemble.Ensemble(dyn, 0, dyn.GetSupercell())
+    ens.load(DATA_PATH, 2, 10)
+
+    minim = sscha.SchaMinimizer.SSCHA_Minimizer(ens)
+
+    cluster = sscha.Cluster.Cluster(hostname="localhost")
+    relax = sscha.Relax.SSCHA(minim, N_configs=10, max_pop=2,
+                              cluster=cluster)
+
+    # Cluster.compute_ensemble_batch leaves a threading.Lock on the
+    # cluster after the ensemble calculation; reproduce that state.
+    relax.cluster.lock = threading.Lock()
+
+    with tempfile.TemporaryDirectory() as tmpdir:
+        filename = os.path.join(tmpdir, "relax.bin")
+        sscha.Utilities.save_binary(relax, filename)
+
+        loaded = sscha.Utilities.load_binary(filename)
+
+    # The lock is transient runtime state and must come back unset.
+    assert loaded.cluster.lock is None
+    assert loaded.cluster.hostname == "localhost"
+    assert loaded.N_configs == relax.N_configs
+    assert loaded.minim.ensemble.N == ens.N
+
+    if verbose:
+        print("save_binary/load_binary round trip succeeded")
+
+
+if __name__ == "__main__":
+    test_save_binary_relax_with_cluster(True)