diff --git a/pyproject.toml b/pyproject.toml
index c68aa79..5fa84f7 100644
--- a/pyproject.toml
+++ b/pyproject.toml
@@ -49,6 +49,9 @@ optional-dependencies.dev = [
     "interrogate==1.7.0",
     "mypy[faster-cache]==1.14.1",
     "mypy-strict-kwargs==2024.12.25",
+    # Dependency of mypy[faster-cache].
+    # Versioned here to work around https://github.com/ijl/orjson/issues/548
+    "orjson==3.10.14",
     "pre-commit==4.0.1",
     "pylint==3.3.3",
     "pyproject-fmt==2.5.0",