Fix issue #139; Version 1.9.0 #274

Job	Run time
test_matrix (ubuntu, 2.5)	29s
test_matrix (ubuntu, 2.6)	31s
test_matrix (ubuntu, 2.7)	28s
test_matrix (ubuntu, 3.0)	19s
test_matrix (ubuntu, 3.1)	16s
test_matrix (ubuntu, 3.2)	1s
test_matrix (ubuntu, head)	27s
test_matrix (ubuntu, truffleruby)	9s
test_matrix (ubuntu, truffleruby-head)	1m 6s
test_matrix (macos, 2.5)	1m 12s
test_matrix (macos, 2.6)	1m 6s
test_matrix (macos, 2.7)	21s
test_matrix (macos, 3.0)	27s
test_matrix (macos, 3.1)	3s
test_matrix (macos, 3.2)	33s
test_matrix (macos, head)	21s
test_matrix (macos, truffleruby)	10s
test_matrix (macos, truffleruby-head)	1m 34s
finish	0s
	9m 33s

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