1 files changed, 4 insertions, 0 deletions
diff --git a/test/test_cmath.rb b/test/test_cmath.rb
index 4f85ec3d04..ae4b15cafe 100644
--- a/test/test_cmath.rb
+++ b/test/test_cmath.rb
@@ -6,6 +6,10 @@ class TestCMath < Test::Unit::TestCase
     assert_equal CMath.sqrt(1.0.i), CMath.sqrt(1.i), '[ruby-core:31672]'
   end
 
+  def test_acos
+    assert_equal Complex(0.9368124611557199,-2.305509031243477), CMath.acos(Complex(3, 4))
+  end
+
   def test_cbrt_returns_principal_value_of_cube_root
     assert_equal CMath.cbrt(-8), (-8)**(1.0/3), '#3676'
   end