diff --git a/requirements.testing.txt b/requirements.testing.txt
index 4e2c0b2f..38866fb3 100644
--- a/requirements.testing.txt
+++ b/requirements.testing.txt
@@ -1,7 +1,7 @@
 pytest>=8.4.0
 codecov>=2.1.13
 pytest-cov>=5.0.0
-packaging
+packaging==26.2
 mdtraj>=1.10.2
 openmm
 build