diff --git a/CHANGES.md b/CHANGES.md
index 58e3f60d..13b7e279 100644
--- a/CHANGES.md
+++ b/CHANGES.md
@@ -2,6 +2,10 @@
 
 ### Unreleased
 
+### 2025-07-28 (2.13.2)
+
+* Improve duplicate key warning and errors to include the key name and point to the right caller.
+
 ### 2025-07-24 (2.13.1)
 
 * Fix support for older compilers without `__builtin_cpu_supports`.
diff --git a/ext/json/ext/parser/parser.c b/ext/json/ext/parser/parser.c
index 01b6e629..ab9d6c20 100644
--- a/ext/json/ext/parser/parser.c
+++ b/ext/json/ext/parser/parser.c
@@ -422,10 +422,12 @@ static void emit_parse_warning(const char *message, JSON_ParserState *state)
     long line, column;
     cursor_position(state, &line, &column);
 
-    rb_warn("%s at line %ld column %ld", message, line, column);
+    VALUE warning = rb_sprintf("%s at line %ld column %ld", message, line, column);
+    rb_funcall(mJSON, rb_intern("deprecation_warning"), 1, warning);
 }
 
 #define PARSE_ERROR_FRAGMENT_LEN 32
+
 #ifdef RBIMPL_ATTR_NORETURN
 RBIMPL_ATTR_NORETURN()
 #endif
@@ -830,21 +832,64 @@ static inline VALUE json_decode_array(JSON_ParserState *state, JSON_ParserConfig
     return array;
 }
 
+static VALUE json_find_duplicated_key(size_t count, const VALUE *pairs)
+{
+    VALUE set = rb_hash_new_capa(count / 2);
+    for (size_t index = 0; index < count; index += 2) {
+        size_t before = RHASH_SIZE(set);
+        VALUE key = pairs[index];
+        rb_hash_aset(set, key, Qtrue);
+        if (RHASH_SIZE(set) == before) {
+            if (RB_SYMBOL_P(key)) {
+                return rb_sym2str(key);
+            }
+            return key;
+        }
+    }
+    return Qfalse;
+}
+
+static void emit_duplicate_key_warning(JSON_ParserState *state, VALUE duplicate_key)
+{
+    VALUE message = rb_sprintf(
+        "detected duplicate key %"PRIsVALUE" in JSON object. This will raise an error in json 3.0 unless enabled via `allow_duplicate_key: true`",
+        rb_inspect(duplicate_key)
+    );
+
+    emit_parse_warning(RSTRING_PTR(message), state);
+    RB_GC_GUARD(message);
+}
+
+#ifdef RBIMPL_ATTR_NORETURN
+RBIMPL_ATTR_NORETURN()
+#endif
+static void raise_duplicate_key_error(JSON_ParserState *state, VALUE duplicate_key)
+{
+    VALUE message = rb_sprintf(
+        "duplicate key %"PRIsVALUE,
+        rb_inspect(duplicate_key)
+    );
+
+    raise_parse_error(RSTRING_PTR(message), state);
+    RB_GC_GUARD(message);
+}
+
 static inline VALUE json_decode_object(JSON_ParserState *state, JSON_ParserConfig *config, size_t count)
 {
     size_t entries_count = count / 2;
     VALUE object = rb_hash_new_capa(entries_count);
-    rb_hash_bulk_insert(count, rvalue_stack_peek(state->stack, count), object);
+    const VALUE *pairs = rvalue_stack_peek(state->stack, count);
+    rb_hash_bulk_insert(count, pairs, object);
 
     if (RB_UNLIKELY(RHASH_SIZE(object) < entries_count)) {
         switch (config->on_duplicate_key) {
             case JSON_IGNORE:
                 break;
             case JSON_DEPRECATED:
-                emit_parse_warning("detected duplicate keys in JSON object. This will raise an error in json 3.0 unless enabled via `allow_duplicate_key: true`", state);
+                emit_duplicate_key_warning(state, json_find_duplicated_key(count, pairs));
                 break;
             case JSON_RAISE:
-                raise_parse_error("duplicate key", state);
+                raise_duplicate_key_error(state, json_find_duplicated_key(count, pairs));
                 break;
         }
     }
diff --git a/ext/json/ext/simd/simd.h b/ext/json/ext/simd/simd.h
index f8503d13..3abbdb02 100644
--- a/ext/json/ext/simd/simd.h
+++ b/ext/json/ext/simd/simd.h
@@ -7,45 +7,45 @@ typedef enum {
 #ifdef JSON_ENABLE_SIMD
 
 #ifdef __clang__
-  #if __has_builtin(__builtin_ctzll)
-    #define HAVE_BUILTIN_CTZLL 1
-  #else
-    #define HAVE_BUILTIN_CTZLL 0
-  #endif
+# if __has_builtin(__builtin_ctzll)
+#   define HAVE_BUILTIN_CTZLL 1
+# else
+#   define HAVE_BUILTIN_CTZLL 0
+# endif
 #elif defined(__GNUC__) && (__GNUC__ > 4 || (__GNUC__ == 4 && __GNUC_MINOR__ >= 3))
-  #define HAVE_BUILTIN_CTZLL 1
+# define HAVE_BUILTIN_CTZLL 1
 #else
-  #define HAVE_BUILTIN_CTZLL 0
+# define HAVE_BUILTIN_CTZLL 0
 #endif
 
 static inline uint32_t trailing_zeros64(uint64_t input)
 {
 #if HAVE_BUILTIN_CTZLL
-  return __builtin_ctzll(input);
+    return __builtin_ctzll(input);
 #else
-  uint32_t trailing_zeros = 0;
-  uint64_t temp = input;
-  while ((temp & 1) == 0 && temp > 0) {
-    trailing_zeros++;
-    temp >>= 1;
-  }
-  return trailing_zeros;
+    uint32_t trailing_zeros = 0;
+    uint64_t temp = input;
+    while ((temp & 1) == 0 && temp > 0) {
+        trailing_zeros++;
+        temp >>= 1;
+    }
+    return trailing_zeros;
 #endif
 }
 
 static inline int trailing_zeros(int input)
 {
-  #if HAVE_BUILTIN_CTZLL
+#if HAVE_BUILTIN_CTZLL
     return __builtin_ctz(input);
-  #else
+#else
     int trailing_zeros = 0;
     int temp = input;
     while ((temp & 1) == 0 && temp > 0) {
-      trailing_zeros++;
-      temp >>= 1;
+        trailing_zeros++;
+        temp >>= 1;
     }
     return trailing_zeros;
-  #endif
+#endif
 }
 
 #if (defined(__GNUC__ ) || defined(__clang__))
@@ -79,37 +79,38 @@ static inline FORCE_INLINE uint64_t neon_match_mask(uint8x16_t matches)
 
 static inline FORCE_INLINE uint64_t compute_chunk_mask_neon(const char *ptr)
 {
-  uint8x16_t chunk = vld1q_u8((const unsigned char *)ptr);
+    uint8x16_t chunk = vld1q_u8((const unsigned char *)ptr);
 
-  // Trick: c < 32 || c == 34 can be factored as c ^ 2 < 33
-  // https://lemire.me/blog/2025/04/13/detect-control-characters-quotes-and-backslashes-efficiently-using-swar/
-  const uint8x16_t too_low_or_dbl_quote = vcltq_u8(veorq_u8(chunk, vdupq_n_u8(2)), vdupq_n_u8(33));
+    // Trick: c < 32 || c == 34 can be factored as c ^ 2 < 33
+    // https://lemire.me/blog/2025/04/13/detect-control-characters-quotes-and-backslashes-efficiently-using-swar/
+    const uint8x16_t too_low_or_dbl_quote = vcltq_u8(veorq_u8(chunk, vdupq_n_u8(2)), vdupq_n_u8(33));
 
-  uint8x16_t has_backslash = vceqq_u8(chunk, vdupq_n_u8('\\'));
-  uint8x16_t needs_escape  = vorrq_u8(too_low_or_dbl_quote, has_backslash);
-  return neon_match_mask(needs_escape);
+    uint8x16_t has_backslash = vceqq_u8(chunk, vdupq_n_u8('\\'));
+    uint8x16_t needs_escape  = vorrq_u8(too_low_or_dbl_quote, has_backslash);
+    return neon_match_mask(needs_escape);
 }
 
 static inline FORCE_INLINE int string_scan_simd_neon(const char **ptr, const char *end, uint64_t *mask)
 {
     while (*ptr + sizeof(uint8x16_t) <= end) {
-      uint64_t chunk_mask = compute_chunk_mask_neon(*ptr);
-      if (chunk_mask) {
-          *mask = chunk_mask;
-          return 1;
-      }
-      *ptr += sizeof(uint8x16_t);
+        uint64_t chunk_mask = compute_chunk_mask_neon(*ptr);
+        if (chunk_mask) {
+            *mask = chunk_mask;
+            return 1;
+        }
+        *ptr += sizeof(uint8x16_t);
     }
     return 0;
 }
 
-uint8x16x4_t load_uint8x16_4(const unsigned char *table) {
-  uint8x16x4_t tab;
-  tab.val[0] = vld1q_u8(table);
-  tab.val[1] = vld1q_u8(table+16);
-  tab.val[2] = vld1q_u8(table+32);
-  tab.val[3] = vld1q_u8(table+48);
-  return tab;
+static inline uint8x16x4_t load_uint8x16_4(const unsigned char *table)
+{
+    uint8x16x4_t tab;
+    tab.val[0] = vld1q_u8(table);
+    tab.val[1] = vld1q_u8(table+16);
+    tab.val[2] = vld1q_u8(table+32);
+    tab.val[3] = vld1q_u8(table+48);
+    return tab;
 }
 
 #endif /* ARM Neon Support.*/
@@ -150,12 +151,12 @@ static inline TARGET_SSE2 FORCE_INLINE int compute_chunk_mask_sse2(const char *p
 static inline TARGET_SSE2 FORCE_INLINE int string_scan_simd_sse2(const char **ptr, const char *end, int *mask)
 {
     while (*ptr + sizeof(__m128i) <= end) {
-      int chunk_mask = compute_chunk_mask_sse2(*ptr);
-      if (chunk_mask) {
-          *mask = chunk_mask;
-          return 1;
-      }
-      *ptr += sizeof(__m128i);
+        int chunk_mask = compute_chunk_mask_sse2(*ptr);
+        if (chunk_mask) {
+            *mask = chunk_mask;
+            return 1;
+        }
+        *ptr += sizeof(__m128i);
     }
 
     return 0;
diff --git a/java/src/json/ext/ParserConfig.java b/java/src/json/ext/ParserConfig.java
index ccfc558e..2bd03bab 100644
--- a/java/src/json/ext/ParserConfig.java
+++ b/java/src/json/ext/ParserConfig.java
@@ -2125,10 +2125,10 @@ else if ( _widec > _JSON_object_trans_keys[_mid+1] )
                         if (((RubyHash)result).hasKey(lastName)) {
                             if (config.deprecateDuplicateKey) {
                                 context.runtime.getWarnings().warning(
-                                    "detected duplicate keys in JSON object. This will raise an error in json 3.0 unless enabled via `allow_duplicate_key: true`"
+                                    "detected duplicate key " + name.inspect() + " in JSON object. This will raise an error in json 3.0 unless enabled via `allow_duplicate_key: true`"
                                 );
                             } else {
-                                throw parsingError(context, "duplicate key", p, pe);
+                                throw parsingError(context, "duplicate key" + name.inspect(), p, pe);
                             }
                         }
                     }
diff --git a/java/src/json/ext/ParserConfig.rl b/java/src/json/ext/ParserConfig.rl
index 4bc5d93b..533b1322 100644
--- a/java/src/json/ext/ParserConfig.rl
+++ b/java/src/json/ext/ParserConfig.rl
@@ -692,10 +692,10 @@ public class ParserConfig extends RubyObject {
                         if (((RubyHash)result).hasKey(lastName)) {
                             if (config.deprecateDuplicateKey) {
                                 context.runtime.getWarnings().warning(
-                                    "detected duplicate keys in JSON object. This will raise an error in json 3.0 unless enabled via `allow_duplicate_key: true`"
+                                    "detected duplicate key " + name.inspect() + " in JSON object. This will raise an error in json 3.0 unless enabled via `allow_duplicate_key: true`"
                                 );
                             } else {
-                                throw parsingError(context, "duplicate key", p, pe);
+                                throw parsingError(context, "duplicate key" + name.inspect(), p, pe);
                             }
                         }
                     }
diff --git a/lib/json/common.rb b/lib/json/common.rb
index 486ec62a..9a878cea 100644
--- a/lib/json/common.rb
+++ b/lib/json/common.rb
@@ -48,7 +48,7 @@ def array_class_proc(array_class, on_load)
         end
       end
 
-      # TODO: exctract :create_additions support to another gem for version 3.0
+      # TODO: extract :create_additions support to another gem for version 3.0
       def create_additions_proc(opts)
         if opts[:symbolize_names]
           raise ArgumentError, "options :symbolize_names and :create_additions cannot be  used in conjunction"
@@ -87,31 +87,32 @@ def create_additions_proc(opts)
         opts
       end
 
-      GEM_ROOT = File.expand_path("../../../", __FILE__) + "/"
       def create_additions_warning
-        message = "JSON.load implicit support for `create_additions: true` is deprecated " \
+        JSON.deprecation_warning "JSON.load implicit support for `create_additions: true` is deprecated " \
           "and will be removed in 3.0, use JSON.unsafe_load or explicitly " \
           "pass `create_additions: true`"
+      end
+    end
+  end
 
-        uplevel = 4
-        caller_locations(uplevel, 10).each do |frame|
-          if frame.path.nil? || frame.path.start_with?(GEM_ROOT) || frame.path.end_with?("/truffle/cext_ruby.rb", ".c")
-            uplevel += 1
-          else
-            break
-          end
-        end
-
-        if RUBY_VERSION >= "3.0"
-          warn(message, uplevel: uplevel - 1, category: :deprecated)
+  class << self
+    def deprecation_warning(message, uplevel = 3) # :nodoc:
+      gem_root = File.expand_path("../../../", __FILE__) + "/"
+      caller_locations(uplevel, 10).each do |frame|
+        if frame.path.nil? || frame.path.start_with?(gem_root) || frame.path.end_with?("/truffle/cext_ruby.rb", ".c")
+          uplevel += 1
         else
-          warn(message, uplevel: uplevel - 1)
+          break
         end
       end
+
+      if RUBY_VERSION >= "3.0"
+        warn(message, uplevel: uplevel, category: :deprecated)
+      else
+        warn(message, uplevel: uplevel)
+      end
     end
-  end
 
-  class << self
     # :call-seq:
     #   JSON[object] -> new_array or new_string
     #
diff --git a/lib/json/version.rb b/lib/json/version.rb
index 2aef3d7f..f9ac3e17 100644
--- a/lib/json/version.rb
+++ b/lib/json/version.rb
@@ -1,5 +1,5 @@
 # frozen_string_literal: true
 
 module JSON
-  VERSION = '2.13.1'
+  VERSION = '2.13.2'
 end
diff --git a/test/json/json_parser_test.rb b/test/json/json_parser_test.rb
index 106492e1..6455d297 100644
--- a/test/json/json_parser_test.rb
+++ b/test/json/json_parser_test.rb
@@ -333,11 +333,36 @@ def test_parse_big_integers
 
   def test_parse_duplicate_key
     expected = {"a" => 2}
+    expected_sym = {a: 2}
+
     assert_equal expected, parse('{"a": 1, "a": 2}', allow_duplicate_key: true)
     assert_raise(ParserError) { parse('{"a": 1, "a": 2}', allow_duplicate_key: false) }
-    assert_deprecated_warning(/duplicate keys/) do
+    assert_raise(ParserError) { parse('{"a": 1, "a": 2}', allow_duplicate_key: false, symbolize_names: true) }
+
+    assert_deprecated_warning(/duplicate key "a"/) do
       assert_equal expected, parse('{"a": 1, "a": 2}')
     end
+    assert_deprecated_warning(/duplicate key "a"/) do
+      assert_equal expected_sym, parse('{"a": 1, "a": 2}', symbolize_names: true)
+    end
+
+    if RUBY_ENGINE == 'RUBY_ENGINE'
+      assert_deprecated_warning(/#{File.basename(__FILE__)}\:#{__LINE__ + 1}/) do
+        assert_equal expected, parse('{"a": 1, "a": 2}')
+      end
+    end
+
+    unless RUBY_ENGINE == 'jruby'
+      assert_raise(ParserError) do
+        fake_key = Object.new
+        JSON.load('{"a": 1, "a": 2}', -> (obj) { obj == "a" ? fake_key : obj }, allow_duplicate_key: false)
+      end
+
+      assert_deprecated_warning(/duplicate key #<Object:0x/) do
+        fake_key = Object.new
+        JSON.load('{"a": 1, "a": 2}', -> (obj) { obj == "a" ? fake_key : obj })
+      end
+    end
   end
 
   def test_some_wrong_inputs