diff --git a/test/test_cmath.rb b/test/test_cmath.rb
index ae4b15cafe..cde1b54be8 100644
--- a/test/test_cmath.rb
+++ b/test/test_cmath.rb
@@ -7,7 +7,9 @@ class TestCMath < Test::Unit::TestCase
   end
 
   def test_acos
-    assert_equal Complex(0.9368124611557199,-2.305509031243477), CMath.acos(Complex(3, 4))
+    c = CMath.acos(Complex(3, 4))
+    assert_in_delta 0.9368124611557199, c.real
+    assert_in_delta -2.305509031243477, c.imag
   end
 
   def test_cbrt_returns_principal_value_of_cube_root