diff --git a/gramps/gen/plug/_manager.py b/gramps/gen/plug/_manager.py
index 8fc4348f7..51bd85a2c 100644
--- a/gramps/gen/plug/_manager.py
+++ b/gramps/gen/plug/_manager.py
@@ -83,7 +83,7 @@ class BasePluginManager:
 
     def __init__(self):
         """ This function should only be run once by get_instance() """
-        if BasePluginManager.__instance is not 1:
+        if BasePluginManager.__instance != 1:
             raise Exception("This class is a singleton. "
                             "Use the get_instance() method")
 
diff --git a/gramps/gen/plug/_pluginreg.py b/gramps/gen/plug/_pluginreg.py
index b2e710fec..10c08db4d 100644
--- a/gramps/gen/plug/_pluginreg.py
+++ b/gramps/gen/plug/_pluginreg.py
@@ -1135,7 +1135,7 @@ class PluginRegister:
 
     def __init__(self):
         """ This function should only be run once by get_instance() """
-        if PluginRegister.__instance is not 1:
+        if PluginRegister.__instance != 1:
             raise Exception("This class is a singleton. "
                             "Use the get_instance() method")
         self.stable_only = True
diff --git a/gramps/gui/pluginmanager.py b/gramps/gui/pluginmanager.py
index df5748001..f2525304d 100644
--- a/gramps/gui/pluginmanager.py
+++ b/gramps/gui/pluginmanager.py
@@ -71,7 +71,7 @@ class GuiPluginManager(Callback):
 
     def __init__(self):
         """ This function should only be run once by get_instance() """
-        if GuiPluginManager.__instance is not 1:
+        if GuiPluginManager.__instance != 1:
             raise Exception("This class is a singleton. "
                             "Use the get_instance() method")