diff --git a/requirements-dev.txt b/requirements-dev.txt
index ca4c02d..b523673 100644
--- a/requirements-dev.txt
+++ b/requirements-dev.txt
@@ -1,4 +1,6 @@
 -r requirements.txt
 httpx>=0.27,<1
+# Starlette's TestClient uses the new httpx2 transport on current releases.
+httpx2>=2.13,<3
 pytest>=8,<9
 ruff>=0.6,<1