--- a/tests/Makefile.am
+++ b/tests/Makefile.am
@@ -26,3 +26,5 @@
 	rm -rf test-log tmp-data tmp.* idx[0-9]* ja-idx[0-9]*
 
 EXTRA_DIST = $(TESTS) select-data commonfuncs
+
+.NOTPARALLEL: