1 files changed, 6 insertions, 2 deletions
diff --git a/test/t/math.rb b/test/t/math.rb
index d71e44fc9..e582c0166 100644
--- a/test/t/math.rb
+++ b/test/t/math.rb
@@ -110,8 +110,12 @@ if Object.const_defined?(:Math)
     check_float(Math.erf(1), 0.842700792949715)
   end
 
-  assert('Math.erfc 1') do
-    check_float(Math.erfc(1), 0.157299207050285)
+  assert('Math.erf -1') do
+    check_float(Math.erf(-1), -0.8427007929497148)
+  end
+
+  assert('Math.erfc -1') do
+    check_float(Math.erfc(-1), 1.8427007929497148)
   end
 end