diff --git a/CHANGES.md b/CHANGES.md
index 3f455f7c4..13c5e0631 100644
--- a/CHANGES.md
+++ b/CHANGES.md
@@ -2,6 +2,9 @@
 
 ### Unreleased
 
+* Emit a deprecation warning for the outdated `quirks_mode: true` argument.
+* Emit a deprecation for `JSON.dump` positional `limit` argument.
+
 ### 2026-07-31 (2.21.2)
 
 * Fix a use-after-free bug in `JSON::ResumableParser`. [GHSA-9hj4-r449-hfvc][CVE-2026-71847].
diff --git a/lib/json/common.rb b/lib/json/common.rb
index fdcb860db..271f2460d 100644
--- a/lib/json/common.rb
+++ b/lib/json/common.rb
@@ -360,6 +360,9 @@ def to_json(state = nil, *)
   #   JSON.parse('')
   #
   def parse(source, opts = nil)
+    if opts&.key?(:quirks_mode)
+      deprecation_warning("The `quirks_mode` option was removed since json 2.0 and has no effect. It will raise an error on json 3.0")
+    end
     opts = ParserOptions.prepare(opts) unless opts.nil?
     Parser.parse(source, opts)
   end
@@ -451,6 +454,9 @@ def generate(obj, opts = nil)
     if State === opts
       opts.generate(obj)
     else
+      if opts&.key?(:quirks_mode)
+        deprecation_warning("The `quirks_mode` option was removed since json 2.0 and has no effect. It will raise an error on json 3.0")
+      end
       State.generate(obj, opts, nil)
     end
   end
@@ -960,7 +966,14 @@ def dump(obj, anIO = nil, limit = nil, kwargs = nil)
     end
 
     opts = JSON._dump_default_options
-    opts = opts.merge(:max_nesting => limit) if limit
+    if limit
+      if RUBY_VERSION >= "3.0"
+        warn "JSON.dump's positional `limit` argument is deprecated and will be removed in json 3.0.0. Pass `max_nesting:` instead.", uplevel: 1, category: :deprecated
+      else
+        warn "JSON.dump's positional `limit` argument is deprecated and will be removed in json 3.0.0. Pass `max_nesting:` instead.", uplevel: 1
+      end
+      opts = opts.merge(:max_nesting => limit)
+    end
     opts = opts.merge(kwargs) if kwargs
 
     begin
diff --git a/test/json/json_common_interface_test.rb b/test/json/json_common_interface_test.rb
index 37568b556..ac0d9a150 100644
--- a/test/json/json_common_interface_test.rb
+++ b/test/json/json_common_interface_test.rb
@@ -241,21 +241,37 @@ def test_dump
     obj = eval(too_deep)
     assert_equal too_deep, dump(obj)
     assert_kind_of String, Marshal.dump(obj)
-    assert_raise(ArgumentError) { dump(obj, 100) }
+    assert_deprecated_warning(/max_nesting/) do
+      assert_raise(ArgumentError) { dump(obj, 100) }
+    end
     assert_raise(ArgumentError) { Marshal.dump(obj, 100) }
-    assert_equal too_deep, dump(obj, 101)
+    assert_deprecated_warning(/max_nesting/) do
+      assert_equal too_deep, dump(obj, 101)
+    end
     assert_kind_of String, Marshal.dump(obj, 101)
 
-    assert_equal too_deep, JSON.dump(obj, StringIO.new, 101, strict: false).string
-    assert_equal too_deep, dump(obj, StringIO.new, 101, strict: false).string
-    assert_raise(JSON::GeneratorError) { JSON.dump(Object.new, StringIO.new, 101, strict: true).string }
-    assert_raise(JSON::GeneratorError) { dump(Object.new, StringIO.new, 101, strict: true).string }
+    assert_deprecated_warning(/max_nesting/) do
+      assert_equal too_deep, JSON.dump(obj, StringIO.new, 101, strict: false).string
+    end
+    assert_deprecated_warning(/max_nesting/) do
+      assert_equal too_deep, dump(obj, StringIO.new, 101, strict: false).string
+    end
+    assert_deprecated_warning(/max_nesting/) do
+      assert_raise(JSON::GeneratorError) { JSON.dump(Object.new, StringIO.new, 101, strict: true).string }
+    end
+    assert_deprecated_warning(/max_nesting/) do
+      assert_raise(JSON::GeneratorError) { dump(Object.new, StringIO.new, 101, strict: true).string }
+    end
 
     assert_equal too_deep, dump(obj, nil, nil, strict: false)
-    assert_equal too_deep, dump(obj, nil, 101, strict: false)
+    assert_deprecated_warning(/max_nesting/) do
+      assert_equal too_deep, dump(obj, nil, 101, strict: false)
+    end
     assert_equal too_deep, dump(obj, StringIO.new, nil, strict: false).string
     assert_equal too_deep, dump(obj, nil, strict: false)
-    assert_equal too_deep, dump(obj, 101, strict: false)
+    assert_deprecated_warning(/max_nesting/) do
+      assert_equal too_deep, dump(obj, 101, strict: false)
+    end
     assert_equal too_deep, dump(obj, StringIO.new, strict: false).string
     assert_equal too_deep, dump(obj, strict: false)
   end