diff --git a/src/engine/tasks.cpp b/src/engine/tasks.cpp
index c43f8cc892..fb85d1b6e8 100644
--- a/src/engine/tasks.cpp
+++ b/src/engine/tasks.cpp
@@ -319,7 +319,7 @@ unsigned get_parallelism(int parallelism)
 	#if B2_USE_STD_THREADS
 	return parallelism >= 0
 		? parallelism
-		: std::min(unsigned(globs.jobs), system_info().cpu_thread_count());
+		: std::min(unsigned(globs.jobs), system_info().cpu_thread_count()) - 1;
 	#else
 	return 0;
 	#endif