diff --git a/Lib/test/math_testcases.txt b/Lib/test/math_testcases.txt
index 21730df..be1a49f 100644
--- a/Lib/test/math_testcases.txt
+++ b/Lib/test/math_testcases.txt
@@ -84,6 +84,25 @@
 erf0042 erf -1e150 -> -1.0
 erf0043 erf 1.7e308 -> 1.0
 
+-- Issue 8986: inputs x with exp(-x*x) near the underflow threshold
+-- incorrectly signalled overflow on some platforms.
+erf0100 erf 26.2 -> 1.0
+erf0101 erf 26.4 -> 1.0
+erf0102 erf 26.6 -> 1.0
+erf0103 erf 26.8 -> 1.0
+erf0104 erf 27.0 -> 1.0
+erf0105 erf 27.2 -> 1.0
+erf0106 erf 27.4 -> 1.0
+erf0107 erf 27.6 -> 1.0
+
+erf0110 erf -26.2 -> -1.0
+erf0111 erf -26.4 -> -1.0
+erf0112 erf -26.6 -> -1.0
+erf0113 erf -26.8 -> -1.0
+erf0114 erf -27.0 -> -1.0
+erf0115 erf -27.2 -> -1.0
+erf0116 erf -27.4 -> -1.0
+erf0117 erf -27.6 -> -1.0
 
 ----------------------------------------
 -- erfc: complementary error function --
@@ -127,6 +146,25 @@
 erfc0052 erfc -1e150 -> 2.0
 erfc0053 erfc 1.7e308 -> 0.0
 
+-- Issue 8986: inputs x with exp(-x*x) near the underflow threshold
+-- incorrectly signalled overflow on some platforms.
+erfc0100 erfc 26.2 -> 1.6432507924389461e-300
+erfc0101 erfc 26.4 -> 4.4017768588035426e-305
+erfc0102 erfc 26.6 -> 1.0885125885442269e-309
+erfc0103 erfc 26.8 -> 2.4849621571966629e-314
+erfc0104 erfc 27.0 -> 5.2370464393526292e-319
+erfc0105 erfc 27.2 -> 9.8813129168249309e-324
+erfc0106 erfc 27.4 -> 0.0
+erfc0107 erfc 27.6 -> 0.0
+
+erfc0110 erfc -26.2 -> 2.0
+erfc0111 erfc -26.4 -> 2.0
+erfc0112 erfc -26.6 -> 2.0
+erfc0113 erfc -26.8 -> 2.0
+erfc0114 erfc -27.0 -> 2.0
+erfc0115 erfc -27.2 -> 2.0
+erfc0116 erfc -27.4 -> 2.0
+erfc0117 erfc -27.6 -> 2.0
 
 ---------------------------------------------------------
 -- lgamma: log of absolute value of the gamma function --
diff --git a/Lib/test/test_math.py b/Lib/test/test_math.py
index 36f6847..3049ef1 100644
--- a/Lib/test/test_math.py
+++ b/Lib/test/test_math.py
@@ -996,6 +996,15 @@
                         accuracy_failure = acc_check(expected, got,
                                                   rel_err = 5e-15,
                                                   abs_err = 5e-15)
+                    elif fn == 'erfc':
+                        # erfc has less-than-ideal accuracy for large
+                        # arguments (x ~ 25 or so), mainly due to the
+                        # error involved in computing exp(-x*x).
+                        #
+                        # XXX Would be better to weaken this test only
+                        # for large x, instead of for all x.
+                        accuracy_failure = ulps_check(expected, got, 2000)
+
                     else:
                         accuracy_failure = ulps_check(expected, got, 20)
                     if accuracy_failure is None: