diff --git a/geojson_pydantic/geometries.py b/geojson_pydantic/geometries.py
index e049601..02a3b1c 100644
--- a/geojson_pydantic/geometries.py
+++ b/geojson_pydantic/geometries.py
@@ -2,11 +2,11 @@
 
 import abc
 import json
-from functools import singledispatchmethod
 from typing import Any, Iterator, List, Union
 
 from pydantic import BaseModel, Field, ValidationError, validator
 from pydantic.error_wrappers import ErrorWrapper
+from singledispatchmethod import singledispatchmethod
 
 from geojson_pydantic.types import (
     LinearRing,
diff --git a/pyproject.toml b/pyproject.toml
index a117d4d..f603d50 100644
--- a/pyproject.toml
+++ b/pyproject.toml
@@ -20,7 +20,7 @@ classifiers = [
     "Typing :: Typed",
 ]
 dynamic = ["version"]
-dependencies = ["pydantic"]
+dependencies = ["pydantic", "singledispatchmethod"]
 
 [project.optional-dependencies]
 test = ["pytest", "pytest-cov", "shapely"]