diff --git a/amanuensis/backend/article.py b/amanuensis/backend/article.py
index 973c123..187e9d0 100644
--- a/amanuensis/backend/article.py
+++ b/amanuensis/backend/article.py
@@ -7,7 +7,7 @@ from typing import Optional
 from sqlalchemy import select
 
 from amanuensis.db import *
-from amanuensis.errors import ArgumentError
+from amanuensis.errors import ArgumentError, BackendArgumentTypeError
 
 
 def create(
@@ -21,11 +21,11 @@ def create(
     """
     # Verify argument types are correct
     if not isinstance(lexicon_id, int):
-        raise ArgumentError("lexicon_id")
+        raise BackendArgumentTypeError(int, lexicon_id=lexicon_id)
     if not isinstance(user_id, int):
-        raise ArgumentError("user_id")
+        raise BackendArgumentTypeError(int, user_id=user_id)
     if character_id is not None and not isinstance(character_id, int):
-        raise ArgumentError("character_id")
+        raise BackendArgumentTypeError(int, character_id=character_id)
 
     # Check that the user is a member of this lexicon
     mem: Membership = db(
diff --git a/amanuensis/backend/character.py b/amanuensis/backend/character.py
index 1b87b3b..01f5804 100644
--- a/amanuensis/backend/character.py
+++ b/amanuensis/backend/character.py
@@ -7,7 +7,7 @@ from typing import Optional
 from sqlalchemy import select, func
 
 from amanuensis.db import *
-from amanuensis.errors import ArgumentError
+from amanuensis.errors import ArgumentError, BackendArgumentTypeError
 
 
 def create(
@@ -22,13 +22,13 @@ def create(
     """
     # Verify argument types are correct
     if not isinstance(lexicon_id, int):
-        raise ArgumentError("lexicon_id")
+        raise BackendArgumentTypeError(int, lexicon_id=lexicon_id)
     if not isinstance(user_id, int):
-        raise ArgumentError("user_id")
+        raise BackendArgumentTypeError(int, user_id=user_id)
     if not isinstance(name, str):
-        raise ArgumentError("name")
+        raise BackendArgumentTypeError(str, name=name)
     if signature is not None and not isinstance(signature, str):
-        raise ArgumentError("signature")
+        raise BackendArgumentTypeError(str, signature=signature)
 
     # Verify character name is valid
     if not name.strip():
diff --git a/amanuensis/backend/index.py b/amanuensis/backend/index.py
index 7f108ec..bfd259c 100644
--- a/amanuensis/backend/index.py
+++ b/amanuensis/backend/index.py
@@ -6,7 +6,7 @@ import re
 from typing import Optional
 
 from amanuensis.db import DbContext, ArticleIndex, IndexType
-from amanuensis.errors import ArgumentError
+from amanuensis.errors import ArgumentError, BackendArgumentTypeError
 
 
 def create(
@@ -23,17 +23,17 @@ def create(
     """
     # Verify argument types are correct
     if not isinstance(lexicon_id, int):
-        raise ArgumentError("lexicon_id")
+        raise BackendArgumentTypeError(int, lexicon_id=lexicon_id)
     if not isinstance(index_type, IndexType):
-        raise ArgumentError("index_type")
+        raise BackendArgumentTypeError(IndexType, index_type=index_type)
     if not isinstance(pattern, str):
-        raise ArgumentError("pattern")
+        raise BackendArgumentTypeError(str, pattern=pattern)
     if not isinstance(logical_order, int):
-        raise ArgumentError("logical_order")
+        raise BackendArgumentTypeError(int, logical_order=logical_order)
     if not isinstance(display_order, int):
-        raise ArgumentError("display_order")
+        raise BackendArgumentTypeError(int, display_order=display_order)
     if capacity is not None and not isinstance(capacity, int):
-        raise ArgumentError("capacity")
+        raise BackendArgumentTypeError(int, capacity=capacity)
 
     # Verify the pattern is valid for the index type:
     if index_type == IndexType.CHAR:
diff --git a/amanuensis/backend/lexicon.py b/amanuensis/backend/lexicon.py
index 073a4cf..ff83b34 100644
--- a/amanuensis/backend/lexicon.py
+++ b/amanuensis/backend/lexicon.py
@@ -8,7 +8,7 @@ from typing import Sequence, Optional
 from sqlalchemy import select, func
 
 from amanuensis.db import DbContext, Lexicon, Membership
-from amanuensis.errors import ArgumentError
+from amanuensis.errors import ArgumentError, BackendArgumentTypeError
 
 
 RE_ALPHANUM_DASH_UNDER = re.compile(r"^[A-Za-z0-9-_]*$")
@@ -25,7 +25,7 @@ def create(
     """
     # Verify name
     if not isinstance(name, str):
-        raise ArgumentError("Lexicon name must be a string")
+        raise BackendArgumentTypeError(str, name=name)
     if not name.strip():
         raise ArgumentError("Lexicon name must not be blank")
     if not RE_ALPHANUM_DASH_UNDER.match(name):
@@ -34,12 +34,12 @@ def create(
         )
 
     # Verify title
-    if title is not None and not isinstance(name, str):
-        raise ArgumentError("Lexicon name must be a string")
+    if title is not None and not isinstance(title, str):
+        raise BackendArgumentTypeError(str, title=title)
 
     # Verify prompt
     if not isinstance(prompt, str):
-        raise ArgumentError("Lexicon prompt must be a string")
+        raise BackendArgumentTypeError(str, prompt=prompt)
 
     # Query the db to make sure the lexicon name isn't taken
     if db(select(func.count(Lexicon.id)).where(Lexicon.name == name)).scalar() > 0:
diff --git a/amanuensis/backend/membership.py b/amanuensis/backend/membership.py
index 5e9af13..baddcdd 100644
--- a/amanuensis/backend/membership.py
+++ b/amanuensis/backend/membership.py
@@ -6,7 +6,7 @@ from sqlalchemy import select, func
 
 from amanuensis.db import DbContext, Membership
 from amanuensis.db.models import Lexicon
-from amanuensis.errors import ArgumentError
+from amanuensis.errors import ArgumentError, BackendArgumentTypeError
 
 
 def create(
@@ -20,11 +20,11 @@ def create(
     """
     # Verify argument types are correct
     if not isinstance(user_id, int):
-        raise ArgumentError("user_id")
+        raise BackendArgumentTypeError(int, user_id=user_id)
     if not isinstance(lexicon_id, int):
-        raise ArgumentError("lexicon_id")
+        raise BackendArgumentTypeError(int, lexicon_id=lexicon_id)
     if not isinstance(is_editor, bool):
-        raise ArgumentError("is_editor")
+        raise BackendArgumentTypeError(bool, is_editor=is_editor)
 
     # Verify user has not already joined lexicon
     if (
diff --git a/amanuensis/backend/post.py b/amanuensis/backend/post.py
index 0a6373f..8a4d59d 100644
--- a/amanuensis/backend/post.py
+++ b/amanuensis/backend/post.py
@@ -8,7 +8,7 @@ from sqlalchemy import select
 
 from amanuensis.db import DbContext, Post
 from amanuensis.db.models import Lexicon
-from amanuensis.errors import ArgumentError
+from amanuensis.errors import ArgumentError, BackendArgumentTypeError
 
 
 def create(
@@ -23,15 +23,15 @@ def create(
 
     # Verify lexicon id
     if not isinstance(lexicon_id, int):
-        raise ArgumentError("Lexicon id must be an integer.")
+        raise BackendArgumentTypeError(int, lexicon_id=lexicon_id)
 
     # Verify user_id
-    if not (isinstance(user_id, int) or user_id is None):
-        raise ArgumentError("User id must be an integer.")
+    if user_id is not None and not isinstance(user_id, int):
+        raise BackendArgumentTypeError(int, user_id=user_id)
 
     # Verify body
     if not isinstance(body, str):
-        raise ArgumentError("Post body must be a string.")
+        raise BackendArgumentTypeError(str, body=body)
     if not body.strip():
         raise ArgumentError("Post body cannot be empty.")
 
diff --git a/amanuensis/backend/user.py b/amanuensis/backend/user.py
index 5542c8c..e07e315 100644
--- a/amanuensis/backend/user.py
+++ b/amanuensis/backend/user.py
@@ -10,7 +10,7 @@ from sqlalchemy import select, func, update
 from werkzeug.security import generate_password_hash, check_password_hash
 
 from amanuensis.db import DbContext, User
-from amanuensis.errors import ArgumentError
+from amanuensis.errors import ArgumentError, BackendArgumentTypeError
 
 
 RE_NO_LETTERS = re.compile(r"^[0-9-_]*$")
@@ -30,7 +30,7 @@ def create(
     """
     # Verify username
     if not isinstance(username, str):
-        raise ArgumentError("Username must be a string")
+        raise BackendArgumentTypeError(str, username=username)
     if len(username) < 3 or len(username) > 32:
         raise ArgumentError("Username must be between 3 and 32 characters")
     if RE_NO_LETTERS.match(username):
@@ -42,18 +42,18 @@ def create(
 
     # Verify password
     if not isinstance(password, str):
-        raise ArgumentError("Password must be a string")
+        raise BackendArgumentTypeError(str, password=password)
 
     # Verify display name
     if display_name is not None and not isinstance(display_name, str):
-        raise ArgumentError("Display name must be a string")
+        raise BackendArgumentTypeError(str, display_name=display_name)
     # If display name is not provided, use the username
     if not display_name or not display_name.strip():
         display_name = username
 
     # Verify email
     if not isinstance(email, str):
-        raise ArgumentError("Email must be a string")
+        raise BackendArgumentTypeError(str, email=email)
 
     # Query the db to make sure the username isn't taken
     if db(select(func.count(User.id)).where(User.username == username)).scalar() > 0:
diff --git a/amanuensis/errors.py b/amanuensis/errors.py
index b6a9145..7c35ee1 100644
--- a/amanuensis/errors.py
+++ b/amanuensis/errors.py
@@ -4,8 +4,21 @@ Submodule of custom exception types
 
 
 class AmanuensisError(Exception):
-    """Base class for exceptions in amanuensis"""
+    """Base class for exceptions in Amanuensis"""
 
 
 class ArgumentError(AmanuensisError):
-    """An internal call was made with invalid arguments"""
+    """An internal call was made with invalid arguments."""
+
+
+class BackendArgumentTypeError(ArgumentError):
+    """
+    A call to a backend function was made with a value of an invalid type for the parameter.
+    Specify the invalid parameter and value as a kwarg.
+    """
+    def __init__(self, obj_type, **kwarg):
+        if not kwarg:
+            raise ValueError("Missing kwarg")
+        param, value = next(iter(kwarg.items()))
+        msg = f"Expected {param} of type {obj_type}, got {type(value)}"
+        super().__init__(msg)
diff --git a/tests/backend/test_character.py b/tests/backend/test_character.py
index d6808f4..bf0bb95 100644
--- a/tests/backend/test_character.py
+++ b/tests/backend/test_character.py
@@ -2,7 +2,7 @@ import pytest
 
 from amanuensis.backend import charq
 from amanuensis.db import *
-from amanuensis.errors import ArgumentError
+from amanuensis.errors import ArgumentError, BackendArgumentTypeError
 
 
 def test_create_character(db: DbContext, lexicon_with_editor, make):
@@ -20,13 +20,13 @@ def test_create_character(db: DbContext, lexicon_with_editor, make):
     kwargs: dict
 
     # Bad argument types
-    with pytest.raises(ArgumentError):
+    with pytest.raises(BackendArgumentTypeError):
         kwargs = {**defaults, "name": b"bytestring"}
         charq.create(**kwargs)
-    with pytest.raises(ArgumentError):
+    with pytest.raises(BackendArgumentTypeError):
         kwargs = {**defaults, "name": None}
         charq.create(**kwargs)
-    with pytest.raises(ArgumentError):
+    with pytest.raises(BackendArgumentTypeError):
         kwargs = {**defaults, "signature": b"bytestring"}
         charq.create(**kwargs)
 
diff --git a/tests/backend/test_lexicon.py b/tests/backend/test_lexicon.py
index 8cc4f28..dbbb904 100644
--- a/tests/backend/test_lexicon.py
+++ b/tests/backend/test_lexicon.py
@@ -5,7 +5,7 @@ import pytest
 
 from amanuensis.backend import lexiq
 from amanuensis.db import DbContext, Lexicon, User
-from amanuensis.errors import ArgumentError
+from amanuensis.errors import ArgumentError, BackendArgumentTypeError
 from tests.conftest import ObjectFactory
 
 
@@ -20,7 +20,7 @@ def test_create_lexicon(db: DbContext):
     kwargs: dict
 
     # Test name constraints
-    with pytest.raises(ArgumentError):
+    with pytest.raises(BackendArgumentTypeError):
         kwargs = {**defaults, "name": None}
         lexiq.create(**kwargs)
     with pytest.raises(ArgumentError):
diff --git a/tests/backend/test_post.py b/tests/backend/test_post.py
index d66426a..289e989 100644
--- a/tests/backend/test_post.py
+++ b/tests/backend/test_post.py
@@ -3,7 +3,7 @@ import pytest
 from amanuensis.backend import postq
 from amanuensis.db import DbContext
 
-from amanuensis.errors import ArgumentError
+from amanuensis.errors import ArgumentError, BackendArgumentTypeError
 
 
 def test_create_post(db: DbContext, lexicon_with_editor):
@@ -20,19 +20,16 @@ def test_create_post(db: DbContext, lexicon_with_editor):
     kwargs: dict
 
     # ids are integers
-    with pytest.raises(ArgumentError):
+    with pytest.raises(BackendArgumentTypeError):
         kwargs = {**defaults, "user_id": "zero"}
         postq.create(**kwargs)
-    with pytest.raises(ArgumentError):
+    with pytest.raises(BackendArgumentTypeError):
         kwargs = {**defaults, "lexicon_id": "zero"}
         postq.create(**kwargs)
 
     # empty arguments don't work
-    with pytest.raises(ArgumentError):
-        kwargs = {**defaults, "lexicon_id": ""}
-        postq.create(**kwargs)
-    with pytest.raises(ArgumentError):
-        kwargs = {**defaults, "user_id": ""}
+    with pytest.raises(BackendArgumentTypeError):
+        kwargs = {**defaults, "lexicon_id": None}
         postq.create(**kwargs)
     with pytest.raises(ArgumentError):
         kwargs = {**defaults, "body": ""}
diff --git a/tests/backend/test_user.py b/tests/backend/test_user.py
index 43af33f..6cf8f88 100644
--- a/tests/backend/test_user.py
+++ b/tests/backend/test_user.py
@@ -4,7 +4,7 @@ import pytest
 
 from amanuensis.backend import userq
 from amanuensis.db import DbContext, User
-from amanuensis.errors import ArgumentError
+from amanuensis.errors import ArgumentError, BackendArgumentTypeError
 
 
 def test_create_user(db: DbContext):
@@ -33,7 +33,7 @@ def test_create_user(db: DbContext):
         userq.create(**kwargs)
 
     # No password
-    with pytest.raises(ArgumentError):
+    with pytest.raises(BackendArgumentTypeError):
         kwargs = {**defaults, "password": None}
         userq.create(**kwargs)