diff --git a/pyproject.toml b/pyproject.toml
index c7dbaf325b..4c6f32da89 100644
--- a/pyproject.toml
+++ b/pyproject.toml
@@ -83,7 +83,7 @@ strict-openff = [
     "mdanalysis==2.10.0",
     "monty==2026.2.18",
     "openmm-mdanalysis-reporter==0.1.0",
-    "openmm==8.4.0.post2",
+    "openmm==8.5.0",
     "pymatgen==2026.3.23", # EXERCISE CAUTION WHEN UPDATING - open ff is extremely sensitive to pymatgen version
 ]