diff --git a/tests/Makefile b/tests/Makefile
index 6a0def921f..5fad2911fe 100644
--- a/tests/Makefile
+++ b/tests/Makefile
@@ -1,3 +1,4 @@
+THREADS = 1
 VREF = tests/vsynth1/00.pgm
 AREF = tests/data/asynth1.sw