diff --git a/ext/json/generator/generator.c b/ext/json/generator/generator.c
index bdc34b71fe3..32f38a58d4e 100644
--- a/ext/json/generator/generator.c
+++ b/ext/json/generator/generator.c
@@ -1135,13 +1135,28 @@ static void generate_json_true(FBuffer *buffer, struct generate_json_data *data,
     fbuffer_append(buffer, "true", 4);
 }
 
+static void generate_json_rfc8785_number(FBuffer *buffer, VALUE obj)
+{
+    VALUE str = rb_proc_call_with_block(rfc8785_number_formatter_proc, 1, &obj, Qnil);
+    Check_Type(str, T_STRING);
+    fbuffer_append_str(buffer, str);
+}
+
 static void generate_json_fixnum(FBuffer *buffer, struct generate_json_data *data, VALUE obj)
 {
+    if (RB_UNLIKELY(data->state->rfc8785)) {
+        generate_json_rfc8785_number(buffer, obj);
+        return;
+    }
     fbuffer_append_long(buffer, FIX2LONG(obj));
 }
 
 static void generate_json_bignum(FBuffer *buffer, struct generate_json_data *data, VALUE obj)
 {
+    if (RB_UNLIKELY(data->state->rfc8785)) {
+        generate_json_rfc8785_number(buffer, obj);
+        return;
+    }
     VALUE tmp = rb_funcall(obj, i_to_s, 0);
     fbuffer_append_str(buffer, StringValue(tmp));
 }
@@ -1171,9 +1186,7 @@ static void generate_json_float(FBuffer *buffer, struct generate_json_data *data
     }
 
     if (RB_UNLIKELY(data->state->rfc8785)) {
-        VALUE str = rb_proc_call_with_block(rfc8785_number_formatter_proc, 1, &obj, Qnil);
-        Check_Type(str, T_STRING);
-        fbuffer_append_str(buffer, str);
+        generate_json_rfc8785_number(buffer, obj);
         return;
     }
 
diff --git a/ext/json/lib/json.rb b/ext/json/lib/json.rb
index 576d86de9ab..72ca9f1de7d 100644
--- a/ext/json/lib/json.rb
+++ b/ext/json/lib/json.rb
@@ -416,6 +416,8 @@ require 'json/common'
 #   order, allowing for arbitrary sort orders.
 # - Option +rfc8785+ (boolean) controls whether the generated JSON will be canonicalized
 #   as defined in RFC8785.
+#   Integers are converted to Float before formatting and may be rounded.
+#   Integers outside the finite Float range raise JSON::GeneratorError.
 #
 # In this example, +obj+ is used first to generate the shortest
 # \JSON data (no whitespace), then again with all formatting options
diff --git a/ext/json/lib/json/ext.rb b/ext/json/lib/json/ext.rb
index 4443d668704..7382867a2d6 100644
--- a/ext/json/lib/json/ext.rb
+++ b/ext/json/lib/json/ext.rb
@@ -60,6 +60,12 @@ module JSON
 
     # Directly lifted from Gregg Kellogg's json-canonicalization
     generator::State.rfc8785_number_formatter_proc = shareable_lambda(->(num) {
+      if Integer === num
+        if num > Float::MAX || num < -Float::MAX
+          raise GeneratorError.new("Integer out of range for RFC 8785", num)
+        end
+        num = num.to_f
+      end
       if num.zero?
         "0"
       else
diff --git a/test/json/json_generator_test.rb b/test/json/json_generator_test.rb
index 02cff38cda7..ee781194d70 100755
--- a/test/json/json_generator_test.rb
+++ b/test/json/json_generator_test.rb
@@ -1283,6 +1283,48 @@ class JSONGeneratorTest < Test::Unit::TestCase
     $VERBOSE = verbose
   end
 
+  {
+    0 => '0',
+    1 => '1',
+    2**53 - 1 => '9007199254740991',
+    2**53 => '9007199254740992',
+    2**53 + 1 => '9007199254740992',
+    2**53 + 3 => '9007199254740996',
+    2**63 - 1 => '9223372036854776000',
+    2**68 => '295147905179352830000',
+    10**20 => '100000000000000000000',
+    10**21 => '1e+21',
+    Float::MAX.to_i => '1.7976931348623157e+308',
+  }.each do |integer, expected|
+    define_method("test_rfc8785_integer_#{integer}") do
+      [1, -1].each do |sign|
+        number = sign * integer
+        json = sign < 0 && integer != 0 ? "-#{expected}" : expected
+        assert_rfc8785 json, number
+        assert_rfc8785 %({"n":[#{json}]}), { 'n' => [number] }
+        assert_equal json, number.to_json(rfc8785: true)
+        assert_equal json, JSON.generate(number, rfc8785: true, max_nesting: false)
+        assert_equal json, JSON::Coder.new(rfc8785: true).dump(number)
+        io = StringIO.new
+        JSON.dump(number, io, rfc8785: true)
+        assert_equal json, io.string
+        assert_equal number.to_s, JSON.generate(number)
+      end
+    end
+  end
+
+  def test_rfc8785_rejects_out_of_range_integers
+    [Float::MAX.to_i + 1, 10**400].each do |integer|
+      [integer, -integer].each do |number|
+        error = assert_raise(JSON::GeneratorError) { JSON.generate(number, rfc8785: true) }
+        assert_same number, error.invalid_object
+        assert_equal 'Integer out of range for RFC 8785', error.message
+        assert_raise(JSON::GeneratorError) { JSON.dump([number], rfc8785: true) }
+        assert_equal number.to_s, JSON.generate(number)
+      end
+    end
+  end
+
   def test_rfc8785_numbers
     assert_rfc8785 '-9007199254740992', -9007199254740992
     assert_rfc8785 '0', 0