diff --git a/encyclopaedia/book/book_ren.py b/encyclopaedia/book/book_ren.py
index d112b45..741cb72 100644
--- a/encyclopaedia/book/book_ren.py
+++ b/encyclopaedia/book/book_ren.py
@@ -219,10 +219,15 @@ def add_entry(self, entry: 'EncEntry') -> bool:
         Raises:
             AddEntryError
         """
-        if entry.parent is not None and entry.parent != self:
-            raise AddEntryError(
-                f"<{entry}> is already a page of {self.parent}",
-            )
+        if entry.parent is not None:
+            if entry.parent == self:
+                raise AddEntryError(
+                    f"<{entry}> is already a page of <{self}>",
+                )
+            else:
+                raise AddEntryError(
+                    f"<{entry}> already has a parent: <{entry.parent}>",
+                )
 
         if entry.number is None:
             raise AddEntryError(f"<{entry} does not have a number.")
diff --git a/encyclopaedia/encyclopaedia_ren.py b/encyclopaedia/encyclopaedia_ren.py
index 6108de7..affc89d 100644
--- a/encyclopaedia/encyclopaedia_ren.py
+++ b/encyclopaedia/encyclopaedia_ren.py
@@ -17,6 +17,7 @@
     ToggleShowLockedEntryAction,
 )
 from .entry_sorting_ren import push_locked_to_bottom
+from .exceptions_ren import AddEntryError
 from .eventemitter_ren import EventEmitter
 from .constants_ren import Direction, SortMode
 from .book import Book
@@ -253,14 +254,14 @@ def add_entry(self, entry: ENTRY_TYPE) -> None:
             entry: The Entry to add to the Encyclopaedia
         """
         if entry.parent is not None and entry.parent != self:
-            raise ValueError(
-                f"{entry} is already inside another Encyclopaedia",
+            raise AddEntryError(
+                f"<{entry}> already has a parent: <{entry.parent}>",
             )
 
         # When a new entry has a number, ensure it's not already used.
         if entry.number is not None:
             if any(i for i in self.all_entries if i.number == entry.number):
-                raise ValueError(f"{entry.number} is already taken.")
+                raise AddEntryError(f"{entry.number} is already taken.")
 
         elif entry.number is None:
             entry.number = self._find_closest_free_number()
diff --git a/encyclopaedia/exceptions_ren.py b/encyclopaedia/exceptions_ren.py
index e6828ce..934ce81 100644
--- a/encyclopaedia/exceptions_ren.py
+++ b/encyclopaedia/exceptions_ren.py
@@ -3,5 +3,5 @@
 """
 
 class AddEntryError(Exception):
-    """Raised when adding an EncEntry to a parent fails."""
+    """Raised when adding an entry to a parent fails."""
     pass
diff --git a/tests/test_encyclopaedia.py b/tests/test_encyclopaedia.py
index ea801dc..79f4e3c 100644
--- a/tests/test_encyclopaedia.py
+++ b/tests/test_encyclopaedia.py
@@ -3,7 +3,7 @@
 from encyclopaedia import Encyclopaedia
 from encyclopaedia import EncEntry
 from encyclopaedia import constants_ren
-
+from encyclopaedia import exceptions_ren
 
 def test_setting_entry_number(add_dummy_entries):
     """
@@ -248,7 +248,7 @@ def test_duplicate_entry_numbers():
         locked=False,
     )
 
-    with pytest.raises(ValueError) as e:
+    with pytest.raises(exceptions_ren.AddEntryError) as e:
         EncEntry(
             parent=enc,
             number=1,
@@ -444,7 +444,7 @@ def test_add_entry_already_in_page():
         text=["Test Text"],
     )
 
-    with pytest.raises(ValueError):
+    with pytest.raises(exceptions_ren.AddEntryError):
         enc.add_entry(ee)