diff --git a/.github/workflows/CI.yml b/.github/workflows/CI.yml
index 38a82f23a..a55b3642a 100644
--- a/.github/workflows/CI.yml
+++ b/.github/workflows/CI.yml
@@ -27,8 +27,8 @@ jobs:
     strategy:
       fail-fast: false
       matrix:
-        os: [ubuntu-latest, macos-latest]
-        python-version: ["3.10", "3.11", "3.12"]
+        os: [macos-12, macos-13, macos-15]
+        python-version: ["3.10"]
         rdkit: [true, false]
         openeye: [true, false]
         exclude:
diff --git a/devtools/conda-envs/test_env.yaml b/devtools/conda-envs/test_env.yaml
index efca4a510..ecc2fa9b9 100644
--- a/devtools/conda-envs/test_env.yaml
+++ b/devtools/conda-envs/test_env.yaml
@@ -12,7 +12,7 @@ dependencies:
   - cached-property
   - xmltodict
   - python-constraint
-  - openmm =8.1
+  - openmm >=7.6
   - openff-forcefields >=2023.05.1
   - smirnoff99Frosst
   - openff-units =0.2.0