diff --git a/GNUmakefile b/GNUmakefile
index b5cd7cda..b8c533bf 100644
--- a/GNUmakefile
+++ b/GNUmakefile
@@ -172,7 +172,7 @@ endif
 
 # Run the tests.
 .PHONY: tests
-testdir := $(firstword $(wildcard make-test-?.?))
+testdir := $(shell ls -d1 make-test-?.? | sort -n +0.10 -0.11 +0.12 | tail -1l)
 tests: $(testdir)/run_make_tests.pl $(prog)
 	cd $(<D); perl $(<F)