diff --git a/array.c b/array.c
index 9061919bf8..c9bf7659df 100644
--- a/array.c
+++ b/array.c
@@ -5973,6 +5973,20 @@ rb_ary_sum(int argc, VALUE *argv, VALUE ary)
             else
                 goto not_float;
 
+            if (isnan(f)) continue;
+            if (isnan(x)) {
+                f = x;
+                continue;
+            }
+            if (isinf(x)) {
+                if (isinf(f) && signbit(x) != signbit(f))
+                    f = NAN;
+                else
+                    f = x;
+                continue;
+            }
+            if (isinf(f)) continue;
+
             t = f + x;
             if (fabs(f) >= fabs(x))
                 c += ((f - t) + x);
diff --git a/enum.c b/enum.c
index e57fa5ef46..04b6c9cb95 100644
--- a/enum.c
+++ b/enum.c
@@ -3809,6 +3809,25 @@ sum_iter(VALUE i, struct enum_sum_memo *memo)
             goto some_value;
         }
 
+        if (isnan(f)) return;
+        if (isnan(x)) {
+            memo->v = i;
+            memo->f = x;
+            return;
+        }
+        if (isinf(x)) {
+            if (isinf(f) && signbit(x) != signbit(f)) {
+                memo->f = NAN;
+                memo->v = DBL2NUM(f);
+            }
+            else {
+                memo->f = x;
+                memo->v = i;
+            }
+            return;
+        }
+        if (isinf(f)) return;
+
         t = f + x;
         if (fabs(f) >= fabs(x))
             c += ((f - t) + x);
diff --git a/test/ruby/test_array.rb b/test/ruby/test_array.rb
index 7a5fbdb766..9962745f1c 100644
--- a/test/ruby/test_array.rb
+++ b/test/ruby/test_array.rb
@@ -2967,6 +2967,13 @@ class TestArray < Test::Unit::TestCase
     assert_float_equal(large_number+(small_number*10), [large_number/1r, *[small_number]*10].sum)
     assert_float_equal(large_number+(small_number*11), [small_number, large_number/1r, *[small_number]*10].sum)
     assert_float_equal(small_number, [large_number, small_number, -large_number].sum)
+    assert_equal(+Float::INFINITY, [+Float::INFINITY].sum)
+    assert_equal(+Float::INFINITY, [0.0, +Float::INFINITY].sum)
+    assert_equal(+Float::INFINITY, [+Float::INFINITY, 0.0].sum)
+    assert_equal(-Float::INFINITY, [-Float::INFINITY].sum)
+    assert_equal(-Float::INFINITY, [0.0, -Float::INFINITY].sum)
+    assert_equal(-Float::INFINITY, [-Float::INFINITY, 0.0].sum)
+    assert_predicate([-Float::INFINITY, Float::INFINITY].sum, :nan?)
 
     assert_equal("abc", ["a", "b", "c"].sum(""))
     assert_equal([1, [2], 3], [[1], [[2]], [3]].sum([]))
diff --git a/test/ruby/test_enum.rb b/test/ruby/test_enum.rb
index 12fc2ee66a..2167271886 100644
--- a/test/ruby/test_enum.rb
+++ b/test/ruby/test_enum.rb
@@ -966,6 +966,21 @@ class TestEnumerable < Test::Unit::TestCase
     assert_float_equal(large_number+(small_number*11), [small_number, large_number/1r, *[small_number]*10].each.sum)
     assert_float_equal(small_number, [large_number, small_number, -large_number].each.sum)
 
+    k = Class.new do
+      include Enumerable
+      def initialize(*values)
+        @values = values
+      end
+      def each(&block)
+        @values.each(&block)
+      end
+    end
+    assert_equal(+Float::INFINITY, k.new(0.0, +Float::INFINITY).sum)
+    assert_equal(+Float::INFINITY, k.new(+Float::INFINITY, 0.0).sum)
+    assert_equal(-Float::INFINITY, k.new(0.0, -Float::INFINITY).sum)
+    assert_equal(-Float::INFINITY, k.new(-Float::INFINITY, 0.0).sum)
+    assert_predicate(k.new(-Float::INFINITY, Float::INFINITY).sum, :nan?)
+
     assert_equal("abc", ["a", "b", "c"].each.sum(""))
     assert_equal([1, [2], 3], [[1], [[2]], [3]].each.sum([]))
   end