diff --git a/math.c b/math.c
index 898ccb6..fd109eb 100644
--- a/math.c
+++ b/math.c
@@ -75,7 +75,11 @@ math_atan2(VALUE obj, VALUE y, VALUE x)
 	    return DBL2NUM(M_PI);
 	return DBL2NUM(-M_PI);
     }
-    if (isinf(dx) && isinf(dy)) domain_error("atan2");
+    if (isinf(dx) && isinf(dy)) {
+	double dz = (dx < 0.0) ? (3.0 * M_PI / 4.0) : (M_PI / 4.0);
+	if (dy < 0.0) dz = -dz;
+	return DBL2NUM(dz);
+    }
     return DBL2NUM(atan2(dy, dx));
 }
 
diff --git a/test/ruby/test_math.rb b/test/ruby/test_math.rb
index 74b3940..53630d5 100644
--- a/test/ruby/test_math.rb
+++ b/test/ruby/test_math.rb
@@ -21,10 +21,13 @@ def test_atan2
     check(-0.0, Math.atan2(-0.0, +0.0))
     check(+Math::PI, Math.atan2(+0.0, -0.0))
     check(-Math::PI, Math.atan2(-0.0, -0.0))
-    assert_raise(Math::DomainError) { Math.atan2(Float::INFINITY, Float::INFINITY) }
-    assert_raise(Math::DomainError) { Math.atan2(Float::INFINITY, -Float::INFINITY) }
-    assert_raise(Math::DomainError) { Math.atan2(-Float::INFINITY, Float::INFINITY) }
-    assert_raise(Math::DomainError) { Math.atan2(-Float::INFINITY, -Float::INFINITY) }
+    inf = Float::INFINITY
+    expected = 3.0 * Math::PI / 4.0
+    assert_nothing_raised { check(+expected, Math.atan2(+inf, -inf)) }
+    assert_nothing_raised { check(-expected, Math.atan2(-inf, -inf)) }
+    expected = Math::PI / 4.0
+    assert_nothing_raised { check(+expected, Math.atan2(+inf, +inf)) }
+    assert_nothing_raised { check(-expected, Math.atan2(-inf, +inf)) }
     check(0, Math.atan2(0, 1))
     check(Math::PI / 4, Math.atan2(1, 1))
     check(Math::PI / 2, Math.atan2(1, 0))