diff --git a/lib/tfw/components/history_monitor.py b/lib/tfw/components/history_monitor.py
index 9855f57..99add98 100644
--- a/lib/tfw/components/history_monitor.py
+++ b/lib/tfw/components/history_monitor.py
@@ -21,7 +21,6 @@ class HistoryMonitor(ABC, InotifyObserver):
     See examples below.
     """
     def __init__(self, uplink, histfile):
-        self._domain = ''
         self.histfile = histfile
         self.history = []
         self._last_length = len(self.history)
@@ -29,12 +28,9 @@ class HistoryMonitor(ABC, InotifyObserver):
         super().__init__(self.histfile)
 
     @property
+    @abstractmethod
     def domain(self):
-        return self._domain
-
-    @domain.setter
-    def domain(self, domain):
-        self._domain = domain
+        raise NotImplementedError()
 
     def on_modified(self, event):
         self._fetch_history()
@@ -78,9 +74,9 @@ class BashMonitor(HistoryMonitor):
     shopt -s histappend
     unset HISTCONTROL
     """
-    def __init__(self, uplink, histfile):
-        super().__init__(uplink, histfile)
-        self.domain = 'bash'
+    @property
+    def domain(self):
+        return 'bash'
 
     @property
     def command_pattern(self):
@@ -95,9 +91,9 @@ class GDBMonitor(HistoryMonitor):
     HistoryMonitor to monitor GDB sessions.
     For this to work "set trace-commands on" must be set in GDB.
     """
-    def __init__(self, histfile):
-        super().__init__(histfile)
-        self.domain = 'gdb'
+    @property
+    def domain(self):
+        return 'gdb'
 
     @property
     def command_pattern(self):