diff --git a/devtools/conda-envs/test_env.yaml b/devtools/conda-envs/test_env.yaml
index e653eb7..0d9573b 100644
--- a/devtools/conda-envs/test_env.yaml
+++ b/devtools/conda-envs/test_env.yaml
@@ -8,7 +8,7 @@ dependencies:
   - openfe  # TODO: Remove once we don't depend on openfe
   - openff-units
   - openmm
-  - pymbar
+  - pymbar <4
   - pydantic=1  # TODO: Modify when we support pydantic 2
   - python