diff --git a/spoolman/database/filament.py b/spoolman/database/filament.py
index 657101f..8ce8384 100644
--- a/spoolman/database/filament.py
+++ b/spoolman/database/filament.py
@@ -11,7 +11,7 @@ from sqlalchemy.orm import contains_eager, joinedload
 from spoolman.database import models, vendor
 from spoolman.database.utils import (
     SortOrder,
-    add_where_clause,
+    add_where_clause_int_opt,
     add_where_clause_str,
     add_where_clause_str_opt,
     parse_nested_field,
@@ -98,7 +98,7 @@ async def find(
         .join(models.Filament.vendor, isouter=True)
     )
 
-    stmt = add_where_clause(stmt, models.Filament.vendor_id, vendor_id)
+    stmt = add_where_clause_int_opt(stmt, models.Filament.vendor_id, vendor_id)
     stmt = add_where_clause_str(stmt, models.Vendor.name, vendor_name)
     stmt = add_where_clause_str_opt(stmt, models.Filament.name, name)
     stmt = add_where_clause_str_opt(stmt, models.Filament.material, material)
diff --git a/spoolman/database/spool.py b/spoolman/database/spool.py
index d6a9a83..08d97f7 100644
--- a/spoolman/database/spool.py
+++ b/spoolman/database/spool.py
@@ -12,7 +12,8 @@ from sqlalchemy.orm import contains_eager, joinedload
 from spoolman.database import filament, models
 from spoolman.database.utils import (
     SortOrder,
-    add_where_clause,
+    add_where_clause_int,
+    add_where_clause_int_opt,
     add_where_clause_str,
     add_where_clause_str_opt,
     parse_nested_field,
@@ -111,8 +112,8 @@ async def find(
         .options(contains_eager(models.Spool.filament).contains_eager(models.Filament.vendor))
     )
 
-    stmt = add_where_clause(stmt, models.Spool.filament_id, filament_id)
-    stmt = add_where_clause(stmt, models.Filament.vendor_id, vendor_id)
+    stmt = add_where_clause_int(stmt, models.Spool.filament_id, filament_id)
+    stmt = add_where_clause_int_opt(stmt, models.Filament.vendor_id, vendor_id)
     stmt = add_where_clause_str(stmt, models.Vendor.name, vendor_name)
     stmt = add_where_clause_str_opt(stmt, models.Filament.name, filament_name)
     stmt = add_where_clause_str_opt(stmt, models.Filament.material, filament_material)
diff --git a/spoolman/database/utils.py b/spoolman/database/utils.py
index 54e0c90..03cb441 100644
--- a/spoolman/database/utils.py
+++ b/spoolman/database/utils.py
@@ -1,7 +1,7 @@
 """Utility functions for the database module."""
 
 from enum import Enum
-from typing import Any, Optional, TypeVar
+from typing import Any, Optional
 
 import sqlalchemy
 from sqlalchemy import Select
@@ -65,15 +65,26 @@ def add_where_clause_str(
     return stmt
 
 
-T = TypeVar("T")
-
-
-def add_where_clause(
+def add_where_clause_int(
     stmt: Select,
-    field: attributes.InstrumentedAttribute[T],
-    value: Optional[T],
+    field: attributes.InstrumentedAttribute[int],
+    value: Optional[int],
 ) -> Select:
     """Add a where clause to a select statement for a field."""
     if value is not None:
         stmt = stmt.where(field == value)
     return stmt
+
+
+def add_where_clause_int_opt(
+    stmt: Select,
+    field: attributes.InstrumentedAttribute[Optional[int]],
+    value: Optional[int],
+) -> Select:
+    """Add a where clause to a select statement for a field."""
+    if value is not None:
+        if value == -1:
+            stmt = stmt.where(field.is_(None))
+        else:
+            stmt = stmt.where(field == value)
+    return stmt