diff --git a/webviz_subsurface/_providers/ensemble_surface_provider/surface_array_server.py b/webviz_subsurface/_providers/ensemble_surface_provider/surface_array_server.py
index cd3baa744..79d780cea 100644
--- a/webviz_subsurface/_providers/ensemble_surface_provider/surface_array_server.py
+++ b/webviz_subsurface/_providers/ensemble_surface_provider/surface_array_server.py
@@ -61,6 +61,7 @@ def __init__(self, app: Dash) -> None:
                 "CACHE_TYPE": "FileSystemCache",
                 "CACHE_DIR": cache_dir,
                 "CACHE_DEFAULT_TIMEOUT": 0,
+                "CACHE_OPTIONS": {"mode": 0o660},
             }
         )
         self._array_cache.init_app(app.server)