diff --git a/passes/opt/opt_clean/opt_clean.cc b/passes/opt/opt_clean/opt_clean.cc
index 37d58861d..87597d721 100644
--- a/passes/opt/opt_clean/opt_clean.cc
+++ b/passes/opt/opt_clean/opt_clean.cc
@@ -31,7 +31,7 @@ void rmunused_module(RTLIL::Module *module, bool rminit, CleanRunContext &clean_
 
 	// Use no more than one worker per thousand cells, rounded down, so
 	// we only start multithreading with at least 2000 cells.
-	int num_worker_threads = ThreadPool::work_pool_size(0, module->cells_size(), 1000);
+	int num_worker_threads = ThreadPool::work_pool_size(0, module->cells_size(), 10000);
 	ParallelDispatchThreadPool::Subpool subpool(clean_ctx.thread_pool, num_worker_threads);
 	remove_temporary_cells(module, subpool, clean_ctx.flags.verbose);
 	rmunused_module_cells(module, subpool, clean_ctx);
diff --git a/passes/opt/opt_clean/opt_clean.h b/passes/opt/opt_clean/opt_clean.h
index affb217a1..c48a8188a 100644
--- a/passes/opt/opt_clean/opt_clean.h
+++ b/passes/opt/opt_clean/opt_clean.h
@@ -64,7 +64,7 @@ private:
 		int thread_pool_size = 0;
 		for (auto module : selected_modules)
 			thread_pool_size = std::max(thread_pool_size,
-				ThreadPool::work_pool_size(0, module->cells_size(), 1000));
+				ThreadPool::work_pool_size(0, module->cells_size(), 10000));
 		return thread_pool_size;
 	}