diff --git a/entropylab_qpudb/_qpudatabase.py b/entropylab_qpudb/_qpudatabase.py
index 9cc2b1f..8c3e587 100644
--- a/entropylab_qpudb/_qpudatabase.py
+++ b/entropylab_qpudb/_qpudatabase.py
@@ -101,6 +101,10 @@ def create_new_qpu_database(dbname, initial_data_dict, force_create=False, path=
     db_hist.close()
 
 
+class ReadOnlyError(Exception):
+    pass
+
+
 class QpuDatabaseConnectionBase(Instrument):
     def setup_driver(self):
         pass
@@ -143,13 +147,16 @@ def __init__(self, dbname, history_index=None, path=None):
         self._con_hist.transaction_manager.begin()
         hist_entries = self._con_hist.root()["entries"]
         if self._history_index is not None:
+            self._readonly = True
             message_index = self._history_index
             at = self._con_hist.root()["entries"][self._history_index]["timestamp"]
         else:
+            self._readonly = False
             message_index = len(hist_entries) - 1
             at = None
         db = ZODB.DB(dbfilename)
         self._con = db.open(transaction_manager=transaction.TransactionManager(), at=at)
+        assert self._con.isReadOnly() == self._readonly, "internal error: Inconsistent readonly state"
         self._con.transaction_manager.begin()
         print(
             f"opening qpu database {dbname} from "
@@ -159,6 +166,10 @@ def __init__(self, dbname, history_index=None, path=None):
     def __enter__(self):
         return self
 
+    @property
+    def readonly(self):
+        return self._readonly
+
     def close(self):
         print(f"closing qpu database {self._dbname}")
         self._con._db.close()
@@ -182,11 +193,11 @@ def set(self, element, attribute, value, new_cal_state=None):
         root["elements"][element][attribute].cal_state = new_cal_state
 
     def add_attribute(
-        self,
-        element: str,
-        attribute: str,
-        value: Any = None,
-        new_cal_state: Optional[CalState] = None,
+            self,
+            element: str,
+            attribute: str,
+            value: Any = None,
+            new_cal_state: Optional[CalState] = None,
     ) -> None:
         """
         Adds an attribute to an existing element.
@@ -235,6 +246,8 @@ def commit(self, message: Optional[str] = None) -> None:
         Permanently store the existing state to the DB and add a new commit to the history list
         :param message: an optional message for the commit
         """
+        if self._readonly:
+            raise ReadOnlyError("Attempting to commit to a DB in a readonly state")
         self._con.transaction_manager.commit()
         hist_root = self._con_hist.root()
         hist_entries = hist_root["entries"]
diff --git a/entropylab_qpudb/tests/test_qpudatabase.py b/entropylab_qpudb/tests/test_qpudatabase.py
index 5a32bbb..a0f71b7 100644
--- a/entropylab_qpudb/tests/test_qpudatabase.py
+++ b/entropylab_qpudb/tests/test_qpudatabase.py
@@ -4,6 +4,7 @@
 from time import sleep
 
 import pytest
+from persistent.timestamp import _parseRaw
 from quaentropy.instruments.lab_topology import LabResources, ExperimentResources
 from quaentropy.results_backend.sqlalchemy.db import SqlAlchemyDB
 
@@ -11,7 +12,7 @@
 from entropylab_qpudb._qpudatabase import (
     QpuDatabaseConnectionBase,
     create_new_qpu_database,
-    QpuParameter,
+    QpuParameter, ReadOnlyError,
 )
 
 
@@ -164,6 +165,29 @@ def test_set_with_commit_history(testdb):
         print(db.get_history())
 
 
+def test_fail_on_commit_to_readonly(testdb):
+    with QpuDatabaseConnection(testdb, simp_resolver) as db:
+        print()
+        db.set("q2", "p1", 11.0)
+        print(db.get("q2", "p1"))
+        db.commit("my first commit")
+
+    sleep(0.5)
+
+    # open historical connection
+
+    # should fail when DB is modified
+    with QpuDatabaseConnection(testdb, simp_resolver, history_index=0) as db:
+        db.set('q1', 'p1', 444)
+        with pytest.raises(ReadOnlyError):
+            db.commit('trying')
+
+    # should fail when DB is not modified
+    with QpuDatabaseConnection(testdb, simp_resolver, history_index=0) as db:
+        with pytest.raises(ReadOnlyError):
+            db.commit('trying')
+
+
 def test_print(testdb):
     with QpuDatabaseConnectionBase(testdb) as db:
         print()