diff --git a/.gitignore b/.gitignore
index eb279fcf..0bc83f63 100644
--- a/.gitignore
+++ b/.gitignore
@@ -133,3 +133,4 @@ mthree/version.py
 docs/*.json
 docs/stubs/*
 docs/tutorials/
+bad_cals.json
diff --git a/mthree/mitigation.py b/mthree/mitigation.py
index fe1260ae..b0613280 100644
--- a/mthree/mitigation.py
+++ b/mthree/mitigation.py
@@ -67,6 +67,8 @@ def __init__(self, system=None, iter_threshold=4096):
         self._job_error = None
         # Holds the cals file
         self.cals_file = None
+        # faulty qubits
+        self.faulty_qubits = []
 
     def __getattribute__(self, attr):
         """This allows for checking the status of the threaded cals call
@@ -197,6 +199,7 @@ def cals_from_file(self, cals_file):
                 self.cal_shots = None
                 self.single_qubit_cals = [np.asarray(cal) if cal else None
                                           for cal in loaded_data]
+        self.faulty_qubits = _faulty_qubit_checker(self.single_qubit_cals)
 
     def cals_to_file(self, cals_file=None):
         """Save calibration data to JSON file.
@@ -213,7 +216,7 @@ def cals_to_file(self, cals_file=None):
         if not self.single_qubit_cals:
             raise M3Error('Mitigator is not calibrated.')
         save_dict = {'timestamp': self.cal_timestamp,
-                     'backend': self.system_info["name"],
+                     'backend': self.system_info.get("name", None),
                      'shots': self.cal_shots,
                      'cals': self.single_qubit_cals}
         with open(cals_file, 'wb') as fd:
@@ -247,6 +250,7 @@ def cals_from_matrices(self, matrices):
                 raise M3Error('Input list length not equal to'
                               ' number of qubits {} != {}'.format(len(matrices), self.num_qubits))
         self.single_qubit_cals = matrices
+        self.faulty_qubits = _faulty_qubit_checker(self.single_qubit_cals)
 
     def cals_to_matrices(self):
         """Return single qubit cals as list of NumPy arrays
@@ -383,6 +387,15 @@ def apply_correction(self, counts, qubits, distance=None,
         if len(qubits) != len(counts):
             raise M3Error('Length of counts does not match length of qubits.')
 
+        # Check if using faulty qubits
+        bad_qubits = set()
+        for item in qubits:
+            for qu in item:
+                if qu in self.faulty_qubits:
+                    bad_qubits.add(qu)
+        if any(bad_qubits):
+            raise M3Error('Using faulty qubits: {}'.format(bad_qubits))
+
         quasi_out = []
         for idx, cnts in enumerate(counts):
 
@@ -743,19 +756,32 @@ def _job_thread(job, mit, method, qubits, num_cal_qubits, cal_strings):
                 else:
                     cal[1, 1] += good_prep[kk] / denom
 
-        for jj, cal in enumerate(cals):
+        for cal in cals:
             cal[1, 0] = 1.0 - cal[0, 0]
             cal[0, 1] = 1.0 - cal[1, 1]
 
-            if cal[0, 1] >= cal[0, 0]:
-                bad_list.append(qubits[jj])
-
         for idx, cal in enumerate(cals):
             mit.single_qubit_cals[qubits[idx]] = cal
 
     # save cals to file, if requested
     if mit.cals_file:
         mit.cals_to_file(mit.cals_file)
-    # Return list of faulty qubits, if any
-    if any(bad_list):
-        mit._job_error = M3Error('Faulty qubits detected: {}'.format(bad_list))
+    # faulty qubits, if any
+    mit.faulty_qubits = _faulty_qubit_checker(mit.single_qubit_cals)
+
+
+def _faulty_qubit_checker(cals):
+    """Find faulty qubits in cals
+
+    Parameters:
+        cals (list): Input list of calibrations
+
+    Returns:
+        list: Faulty qubits
+    """
+    faulty_qubits = []
+    for idx, cal in enumerate(cals):
+        if cal is not None:
+            if cal[0, 1] >= cal[0, 0]:
+                faulty_qubits.append(idx)
+    return faulty_qubits
diff --git a/mthree/test/test_faulty.py b/mthree/test/test_faulty.py
new file mode 100644
index 00000000..34094313
--- /dev/null
+++ b/mthree/test/test_faulty.py
@@ -0,0 +1,53 @@
+# This code is part of Mthree.
+#
+# (C) Copyright IBM 2023.
+#
+# This code is licensed under the Apache License, Version 2.0. You may
+# obtain a copy of this license in the LICENSE.txt file in the root directory
+# of this source tree or at http://www.apache.org/licenses/LICENSE-2.0.
+#
+# Any modifications or derivative works of this code must retain this
+# copyright notice, and modified files need to carry a notice indicating
+# that they have been altered from the originals.
+# pylint: disable=no-name-in-module
+
+"""Test faulty qubits handling"""
+import numpy as np
+import pytest
+
+import mthree
+
+
+def test_faulty_logic():
+    """Test faulty qubits block correction"""
+
+    mit = mthree.M3Mitigation(None)
+    mit.single_qubit_cals = [np.array([[0.9819, 0.043],
+                                       [0.0181, 0.957]]),
+                             np.array([[0.4849, 0.5233],
+                                       [0.5151, 0.4767]]),
+                             np.array([[0.9092, 0.4021],
+                                       [0.0908, 0.5979]]),
+                             np.array([[0.4117, 0.8101],
+                                       [0.5883, 0.1899]])]
+    mit.faulty_qubits = [1, 3]
+    counts = {"00": 0.4, "01": 0.1, "11": 0.5}
+    with pytest.raises(mthree.exceptions.M3Error) as _:
+        _ = mit.apply_correction(counts, qubits=[3, 2])
+
+
+def test_faulty_io():
+    """Check round-tripping IO still has faulty qubits"""
+    mit = mthree.M3Mitigation(None)
+    mit.single_qubit_cals = [np.array([[0.9819, 0.043],
+                                       [0.0181, 0.957]]),
+                             np.array([[0.4849, 0.5233],
+                                       [0.5151, 0.4767]]),
+                             np.array([[0.9092, 0.4021],
+                                       [0.0908, 0.5979]]),
+                             np.array([[0.4117, 0.8101],
+                                       [0.5883, 0.1899]])]
+    mit.cals_to_file('bad_cals.json')
+    mit2 = mthree.M3Mitigation(None)
+    mit2.cals_from_file('bad_cals.json')
+    assert mit2.faulty_qubits == [1, 3]
diff --git a/setup.py b/setup.py
index 57e7c774..5ef060f7 100644
--- a/setup.py
+++ b/setup.py
@@ -23,7 +23,7 @@
 from Cython.Build import cythonize
 
 MAJOR = 2
-MINOR = 2
+MINOR = 3
 MICRO = 0
 
 ISRELEASED = False