diff --git a/cura/QualityManager.py b/cura/QualityManager.py
index 8aa3c3a097..d7b2c7d705 100644
--- a/cura/QualityManager.py
+++ b/cura/QualityManager.py
@@ -22,7 +22,7 @@ class QualityManager:
             QualityManager.__instance = cls()
         return QualityManager.__instance
 
-    __instance = None   # type: 'QualityManager'
+    __instance = None   # type: "QualityManager"
 
     ##  Find a quality by name for a specific machine definition and materials.
     #
diff --git a/cura/Settings/ContainerManager.py b/cura/Settings/ContainerManager.py
index 061f0f9b79..4e4fc36784 100644
--- a/cura/Settings/ContainerManager.py
+++ b/cura/Settings/ContainerManager.py
@@ -697,7 +697,7 @@ class ContainerManager(QObject):
             ContainerManager.__instance = cls()
         return ContainerManager.__instance
 
-    __instance = None   # type: 'ContainerManager'
+    __instance = None   # type: "ContainerManager"
 
     # Factory function, used by QML
     @staticmethod
diff --git a/cura/Settings/ExtruderManager.py b/cura/Settings/ExtruderManager.py
index 52a2a9c694..add906c166 100644
--- a/cura/Settings/ExtruderManager.py
+++ b/cura/Settings/ExtruderManager.py
@@ -89,7 +89,7 @@ class ExtruderManager(QObject):
     #
     #   \return The extruder manager.
     @classmethod
-    def getInstance(cls) -> 'ExtruderManager':
+    def getInstance(cls) -> "ExtruderManager":
         if not cls.__instance:
             cls.__instance = ExtruderManager()
         return cls.__instance
diff --git a/cura/Settings/ProfilesModel.py b/cura/Settings/ProfilesModel.py
index d60a633549..404bb569a5 100644
--- a/cura/Settings/ProfilesModel.py
+++ b/cura/Settings/ProfilesModel.py
@@ -38,7 +38,7 @@ class ProfilesModel(InstanceContainersModel):
             ProfilesModel.__instance = cls()
         return ProfilesModel.__instance
 
-    __instance = None   # type: 'ProfilesModel'
+    __instance = None   # type: "ProfilesModel"
 
     ##  Fetch the list of containers to display.
     #