diff --git a/GTG/core/base_store.py b/GTG/core/base_store.py
index 975e36532..ca1ab6e91 100644
--- a/GTG/core/base_store.py
+++ b/GTG/core/base_store.py
@@ -49,7 +49,7 @@ def new(self) -> Any:
         raise NotImplemented
 
 
-    def get(self, key: str) -> Any:
+    def get(self, key: UUID) -> Any:
         """Get an item by id."""
 
         return self.lookup[key]
diff --git a/GTG/core/tasks.py b/GTG/core/tasks.py
index a6eecfce5..735f62f10 100644
--- a/GTG/core/tasks.py
+++ b/GTG/core/tasks.py
@@ -753,7 +753,7 @@ def duplicate_for_recurrent(self, task: Task) -> Task:
         return new_task
 
 
-    def new(self, title: str = None, parent: UUID = None) -> Task:
+    def new(self, title: str = None, parent: Optional[UUID] = None) -> Task:
         """Create a new task and add it to the store."""
 
         tid = uuid4()
@@ -777,7 +777,7 @@ def from_xml(self, xml: Element, tag_store: TagStore) -> None:
         elements = list(xml.iter(self.XML_TAG))
 
         for element in elements:
-            tid = element.get('id')
+            tid = UUID(element.get('id'))
             title = element.find('title').text
             status = element.get('status')
 
@@ -841,11 +841,11 @@ def from_xml(self, xml: Element, tag_store: TagStore) -> None:
 
         # All tasks have been added, now we parent them
         for element in elements:
-            parent_tid = element.get('id')
+            parent_tid = UUID(element.get('id'))
             subtasks = element.find('subtasks')
 
             for sub in subtasks.findall('sub'):
-                self.parent(sub.text, parent_tid)
+                self.parent(UUID(sub.text), parent_tid)
 
 
     def to_xml(self) -> Element:
@@ -934,7 +934,7 @@ def _append_to_parent_model(self,task_id: UUID) -> None:
         if not pos[0]: model.append(item)
 
 
-    def add(self, item: Any, parent_id: UUID = None) -> None:
+    def add(self, item: Any, parent_id: Optional[UUID] = None) -> None:
         """Add a task to the taskstore."""
 
         super().add(item, parent_id)
diff --git a/GTG/gtk/editor/taskview.py b/GTG/gtk/editor/taskview.py
index 23dfb3f27..9bbf91d1e 100644
--- a/GTG/gtk/editor/taskview.py
+++ b/GTG/gtk/editor/taskview.py
@@ -21,7 +21,7 @@
 
 import re
 from time import time
-from uuid import uuid4
+from uuid import uuid4, UUID
 import logging
 
 from gi.repository import Gtk, GLib, Gdk, GObject, GtkSource
@@ -417,7 +417,7 @@ def on_checkbox_toggle(self, tid: uuid4) -> None:
         self.process()
 
 
-    def add_checkbox(self, tid: int, start: Gtk.TextIter) -> None:
+    def add_checkbox(self, tid: UUID, start: Gtk.TextIter) -> None:
         """Add a checkbox for a subtask."""
 
         task = self.ds.tasks.lookup[tid]
@@ -483,7 +483,7 @@ def detect_internal_link(self, text: str, start: Gtk.TextIter) -> None:
             url_start.forward_chars(match.start())
             url_end.forward_chars(match.end())
 
-            tid = match.group(0).replace('gtg://', '')
+            tid = UUID(match.group(0).replace('gtg://', ''))
             task = self.ds.tasks.lookup[tid]
 
             if task:
@@ -769,7 +769,7 @@ def insert(self, text: str) -> None:
             # Find the subtasks and store their lines
             if line.lstrip().startswith('{!'):
                 # Get the Task ID
-                tid = line.replace('{! ', '').replace(' !}', '').strip()
+                tid = UUID(line.replace('{! ', '').replace(' !}', '').strip())
 
                 # Remember there's a line for the title at the top
                 real_index = index + 1
diff --git a/tests/core/test_task.py b/tests/core/test_task.py
index a9ab36b1b..fb1bb3aa4 100644
--- a/tests/core/test_task.py
+++ b/tests/core/test_task.py
@@ -430,7 +430,7 @@ def test_xml_load_tree(self):
         task_store.from_xml(parsed_xml, None)
         self.assertEqual(task_store.count(), 4)
         self.assertEqual(task_store.count(root_only=True), 1)
-        self.assertEqual(len(task_store.get(str(TASK_ID_1)).children), 2)
+        self.assertEqual(len(task_store.get(TASK_ID_1).children), 2)
 
 
     def test_xml_load_bad(self):
@@ -478,7 +478,7 @@ def test_xml_load_bad(self):
         </tasklist>
         ''')
 
-        with self.assertRaises(KeyError):
+        with self.assertRaises(ValueError):
             task_store.from_xml(parsed_xml, None)