diff --git a/kmir/src/kmir/_prove.py b/kmir/src/kmir/_prove.py
index d7092247a..624bf3eca 100644
--- a/kmir/src/kmir/_prove.py
+++ b/kmir/src/kmir/_prove.py
@@ -149,6 +149,7 @@ def _prove_parallel(
             'module_name': kmir.definition.main_module_name,
             'bug_report': kmir.bug_report,
             'simplify_each': 30,
+            'haskell_threads': opts.max_workers,
         }
     ) as server: