diff --git a/tests/gen-tests-makefile.sh b/tests/gen-tests-makefile.sh
index e3308506b..a0fb23ac3 100755
--- a/tests/gen-tests-makefile.sh
+++ b/tests/gen-tests-makefile.sh
@@ -9,7 +9,7 @@ generate_target() {
 	echo "all: $target_name"
 	echo ".PHONY: $target_name"
 	echo "$target_name:"
-	printf "\t@%s\n" "$test_command"
+	printf "\t@YOSYS_MAX_THREADS=4 %s\n" "$test_command"
 	printf "\t@echo 'Passed %s'\n" "$target_name"
 }