diff --git a/lib/liquid/standardfilters.rb b/lib/liquid/standardfilters.rb
index 63d080dd1..1ec5636b3 100644
--- a/lib/liquid/standardfilters.rb
+++ b/lib/liquid/standardfilters.rb
@@ -952,11 +952,13 @@ def default(input, default_value = '', options = {})
     # @liquid_syntax array | sum
     # @liquid_return [number]
     def sum(input, property = nil)
+      property = Liquid::Utils.to_s(property)
+
       ary = InputIterator.new(input, context)
       return 0 if ary.empty?
 
       values_for_sum = ary.map do |item|
-        if property.nil?
+        if property.empty?
           item
         elsif item.respond_to?(:[])
           item[property]
diff --git a/test/integration/standard_filter_test.rb b/test/integration/standard_filter_test.rb
index 913dfa25b..5c80fe3ce 100644
--- a/test/integration/standard_filter_test.rb
+++ b/test/integration/standard_filter_test.rb
@@ -1281,6 +1281,17 @@ def test_sum_with_floats_and_indexable_map_values
     assert_template_result("0", "{{ input | sum: 'subtotal' }}", { "input" => input })
   end
 
+  def test_sum_with_non_string_property
+    input = [{ "true" => 1 }, { "1.0" => 0.2, "1" => -0.3 }, { "1..5" => 0.4 }]
+
+    assert_equal(1, @filters.sum(input, true))
+    assert_equal(0.2, @filters.sum(input, 1.0))
+    assert_equal(-0.3, @filters.sum(input, 1))
+    assert_equal(0.4, @filters.sum(input, (1..5)))
+    assert_equal(0, @filters.sum(input, nil))
+    assert_equal(0, @filters.sum(input, ""))
+  end
+
   private
 
   def with_timezone(tz)