diff --git a/src/encoding-convert.js b/src/encoding-convert.js
index 63e9ad8..a7722d0 100644
--- a/src/encoding-convert.js
+++ b/src/encoding-convert.js
@@ -2,6 +2,7 @@ var config = require('./config');
 var util = require('./util');
 var EncodingDetect = require('./encoding-detect');
 var EncodingTable = require('./encoding-table');
+var sjisExt = require('./sjis-ext');
 
 /**
  * JIS to SJIS
@@ -134,7 +135,7 @@ function SJISToJIS(data) {
   var index = 0;
   var len = data && data.length;
   var i = 0;
-  var b1, b2;
+  var b1, b2, remapped;
 
   var esc = [
     0x1B, 0x28, 0x42,
@@ -160,8 +161,15 @@ function SJISToJIS(data) {
         results[results.length] = esc[5];
       }
 
-      b1 <<= 1;
       b2 = data[++i];
+      if (sjisExt.hasCP932DuplicateCode(b1)) {
+        // Remap CP932 duplicate codes and IBM extended characters
+        remapped = sjisExt.remapCP932DuplicateCode(b1, b2);
+        b1 = remapped >> 8;
+        b2 = remapped & 0xFF;
+      }
+
+      b1 <<= 1;
       if (b2 < 0x9F) {
         if (b1 < 0x13F) {
           b1 -= 0xE1;
@@ -211,7 +219,7 @@ function SJISToEUCJP(data) {
   var results = [];
   var len = data && data.length;
   var i = 0;
-  var b1, b2;
+  var b1, b2, remapped;
 
   for (; i < len; i++) {
     b1 = data[i];
@@ -220,6 +228,13 @@ function SJISToEUCJP(data) {
       results[results.length] = b1;
     } else if (b1 >= 0x81) {
       b2 = data[++i];
+      if (sjisExt.hasCP932DuplicateCode(b1)) {
+        // Remap CP932 duplicate codes and IBM extended characters
+        remapped = sjisExt.remapCP932DuplicateCode(b1, b2);
+        b1 = remapped >> 8;
+        b2 = remapped & 0xFF;
+      }
+
       b1 <<= 1;
       if (b2 < 0x9F) {
         if (b1 < 0x13F) {
@@ -380,7 +395,7 @@ function SJISToUTF8(data) {
   var results = [];
   var i = 0;
   var len = data && data.length;
-  var b, b1, b2, u2, u3, jis, utf8;
+  var b, b1, b2, u2, u3, jis, utf8, remapped;
 
   for (; i < len; i++) {
     b = data[i];
@@ -393,9 +408,15 @@ function SJISToUTF8(data) {
       results[results.length] = u2 & 0xFF;
       results[results.length] = u3 & 0xFF;
     } else if (b >= 0x80) {
-      b1 = b << 1;
       b2 = data[++i];
+      if (sjisExt.hasCP932DuplicateCode(b)) {
+        // Remap CP932 duplicate codes and IBM extended characters
+        remapped = sjisExt.remapCP932DuplicateCode(b, b2);
+        b = remapped >> 8;
+        b2 = remapped & 0xFF;
+      }
 
+      b1 = b << 1;
       if (b2 < 0x9F) {
         if (b1 < 0x13F) {
           b1 -= 0xE1;
diff --git a/src/encoding-detect.js b/src/encoding-detect.js
index 292aff0..eb0b766 100644
--- a/src/encoding-detect.js
+++ b/src/encoding-detect.js
@@ -153,32 +153,39 @@ function isEUCJP(data) {
 exports.isEUCJP = isEUCJP;
 
 /**
- * Shift-JIS (SJIS)
+ * SJIS (Shift_JIS)
+ *
+ * Includes CP932 (Windows-31J) extensions:
+ * - NEC special character area (0x8740 - 0x879C)
+ * - NEC-selected IBM extended character area (0xED40 - 0xEEFC)
+ * - User-defined character area (0xF040 - 0xF9FC)
+ * - IBM extended character area (0xFA40 - 0xFC4B)
  */
 function isSJIS(data) {
   var i = 0;
   var len = data && data.length;
-  var b;
+  var b, lead;
 
-  while (i < len && data[i] > 0x80) {
-    if (data[i++] > 0xFF) {
+  for (; i < len; i++) {
+    b = data[i];
+    if (b > 0xFF) {
       return false;
     }
-  }
 
-  for (; i < len; i++) {
-    b = data[i];
     if (b <= 0x80 ||
         (0xA1 <= b && b <= 0xDF)) {
       continue;
     }
 
-    if (b === 0xA0 || b > 0xEF || i + 1 >= len) {
+    if (b === 0xA0 || b > 0xFC || i + 1 >= len) {
       return false;
     }
 
+    lead = b;
     b = data[++i];
-    if (b < 0x40 || b === 0x7F || b > 0xFC) {
+    if (b < 0x40 || b > 0xFC || b === 0x7F ||
+        // IBM extended character area ends at 0xFC4B
+        (lead === 0xFC && b > 0x4B)) {
       return false;
     }
   }
diff --git a/src/sjis-ext.js b/src/sjis-ext.js
new file mode 100644
index 0000000..aa9a092
--- /dev/null
+++ b/src/sjis-ext.js
@@ -0,0 +1,94 @@
+/**
+ * Remapping CP932 (Windows-31J) IBM extended characters (0xFA40 - 0xFC4B)
+ *
+ * Remaps IBM extended characters to their corresponding duplicate codes
+ * before conversion. These characters are also assigned in the NEC special
+ * characters (0x8740 - 0x879C), the NEC-selected IBM extended characters
+ * (0xED40 - 0xEEFC), and JIS X 0208.
+ *
+ * The first 28 characters (0xFA40 - 0xFA5B) have individual mappings defined
+ * in CP932_IBM_EXT_SYMBOL_MAP, and the rest are linearly mapped to 0xED40 - 0xEEEC.
+ */
+var CP932_IBM_EXT_SYMBOL_MAP = [
+  // 0xFA40 - 0xFA49 [ⅰ-ⅹ]
+  0xEEEF, 0xEEF0, 0xEEF1, 0xEEF2, 0xEEF3, 0xEEF4, 0xEEF5, 0xEEF6, 0xEEF7, 0xEEF8,
+  // 0xFA4A - 0xFA53 [Ⅰ-Ⅹ]
+  0x8754, 0x8755, 0x8756, 0x8757, 0x8758, 0x8759, 0x875A, 0x875B, 0x875C, 0x875D,
+  // 0xFA54 - 0xFA57 [￢￤＇＂]
+  0x81CA, 0xEEFA, 0xEEFB, 0xEEFC,
+  // 0xFA58 - 0xFA5B [㈱№℡∵]
+  0x878A, 0x8782, 0x8784, 0x81E6
+];
+
+// The number of IBM extended characters (0xFA40 - 0xFC4B)
+var CP932_IBM_EXT_LEN = 388;
+// The number of valid trail bytes per lead byte (0x40 - 0xFC, except 0x7F)
+var CP932_IBM_EXT_TRAIL_BYTES_LEN = 188;
+
+function remapCP932_IBMExt(b1, b2) {
+  var leadOffset = (b1 - 0xFA) * CP932_IBM_EXT_TRAIL_BYTES_LEN;
+  var trailIndex = b2 - (b2 < 0x7F ? 0x40 : 0x41);
+  var ibmExtIndex = leadOffset + trailIndex;
+
+  if (ibmExtIndex < 0 || ibmExtIndex >= CP932_IBM_EXT_LEN) {
+    return (b1 << 8) | b2;
+  }
+
+  if (ibmExtIndex < CP932_IBM_EXT_SYMBOL_MAP.length) {
+    return CP932_IBM_EXT_SYMBOL_MAP[ibmExtIndex];
+  }
+
+  var necSelectedIbmOffset = ibmExtIndex - CP932_IBM_EXT_SYMBOL_MAP.length;
+
+  // Remap to NEC-selected IBM extended characters (0xED40 - 0xEEEC)
+  b1 = 0xED;
+  if (necSelectedIbmOffset >= CP932_IBM_EXT_TRAIL_BYTES_LEN) {
+    necSelectedIbmOffset -= CP932_IBM_EXT_TRAIL_BYTES_LEN;
+    b1++;
+  }
+
+  b2 = necSelectedIbmOffset + 0x40;
+  if (b2 >= 0x7F) {
+    b2++; // Skip invalid trail byte 0x7F
+  }
+  return (b1 << 8) | b2;
+}
+
+/**
+ * Remapping duplicate codes for CP932 NEC special characters to their
+ * standard JIS X 0208 codes.
+ *
+ * This also includes 0xEEF9 in the NEC-selected IBM extended characters.
+ */
+var CP932_NEC_DUPLICATE_MAP = {
+  0x8790: 0x81E0, // ≒ (NEC special characters)
+  0x8791: 0x81DF, // ≡
+  0x8792: 0x81E7, // ∫
+  0x8795: 0x81E3, // √
+  0x8796: 0x81DB, // ⊥
+  0x8797: 0x81DA, // ∠
+  0x879A: 0x81E6, // ∵
+  0x879B: 0x81BF, // ∩
+  0x879C: 0x81BE, // ∪
+  0xEEF9: 0x81CA  // ￢ (NEC-selected IBM extended characters)
+};
+
+function remapCP932DuplicateCode(b1, b2) {
+  if (b2 < 0x40 || b2 > 0xFC || b2 === 0x7F) {
+    return (b1 << 8) | (b2 & 0xFF);
+  }
+
+  if (b1 >= 0xFA) {
+    return remapCP932_IBMExt(b1, b2);
+  }
+
+  var code = (b1 << 8) | b2;
+  var remapped = CP932_NEC_DUPLICATE_MAP[code];
+  return remapped == null ? code : remapped;
+}
+exports.remapCP932DuplicateCode = remapCP932DuplicateCode;
+
+function hasCP932DuplicateCode(b1) {
+  return b1 >= 0xFA || b1 === 0x87 || b1 === 0xEE;
+}
+exports.hasCP932DuplicateCode = hasCP932DuplicateCode;
diff --git a/tests/cp932-ibm-ext-map.js b/tests/cp932-ibm-ext-map.js
new file mode 100644
index 0000000..877476b
--- /dev/null
+++ b/tests/cp932-ibm-ext-map.js
@@ -0,0 +1,401 @@
+/**
+ * SJIS (CP932) IBM extended characters (0xFA40 - 0xFC4B)
+ *
+ * Generated from CP932.TXT:
+ * https://unicode.org/Public/MAPPINGS/VENDORS/MICSFT/WINDOWS/CP932.TXT
+ *
+ * The keys are the SJIS code points and the values are the Unicode
+ * code points, in the same order as CP932.TXT.
+ *
+ * { SJIS : UNICODE }
+ */
+module.exports = {
+  0xFA40: 0x2170, // ⅰ
+  0xFA41: 0x2171, // ⅱ
+  0xFA42: 0x2172, // ⅲ
+  0xFA43: 0x2173, // ⅳ
+  0xFA44: 0x2174, // ⅴ
+  0xFA45: 0x2175, // ⅵ
+  0xFA46: 0x2176, // ⅶ
+  0xFA47: 0x2177, // ⅷ
+  0xFA48: 0x2178, // ⅸ
+  0xFA49: 0x2179, // ⅹ
+  0xFA4A: 0x2160, // Ⅰ
+  0xFA4B: 0x2161, // Ⅱ
+  0xFA4C: 0x2162, // Ⅲ
+  0xFA4D: 0x2163, // Ⅳ
+  0xFA4E: 0x2164, // Ⅴ
+  0xFA4F: 0x2165, // Ⅵ
+  0xFA50: 0x2166, // Ⅶ
+  0xFA51: 0x2167, // Ⅷ
+  0xFA52: 0x2168, // Ⅸ
+  0xFA53: 0x2169, // Ⅹ
+  0xFA54: 0xFFE2, // ￢
+  0xFA55: 0xFFE4, // ￤
+  0xFA56: 0xFF07, // ＇
+  0xFA57: 0xFF02, // ＂
+  0xFA58: 0x3231, // ㈱
+  0xFA59: 0x2116, // №
+  0xFA5A: 0x2121, // ℡
+  0xFA5B: 0x2235, // ∵
+  0xFA5C: 0x7E8A, // 纊
+  0xFA5D: 0x891C, // 褜
+  0xFA5E: 0x9348, // 鍈
+  0xFA5F: 0x9288, // 銈
+  0xFA60: 0x84DC, // 蓜
+  0xFA61: 0x4FC9, // 俉
+  0xFA62: 0x70BB, // 炻
+  0xFA63: 0x6631, // 昱
+  0xFA64: 0x68C8, // 棈
+  0xFA65: 0x92F9, // 鋹
+  0xFA66: 0x66FB, // 曻
+  0xFA67: 0x5F45, // 彅
+  0xFA68: 0x4E28, // 丨
+  0xFA69: 0x4EE1, // 仡
+  0xFA6A: 0x4EFC, // 仼
+  0xFA6B: 0x4F00, // 伀
+  0xFA6C: 0x4F03, // 伃
+  0xFA6D: 0x4F39, // 伹
+  0xFA6E: 0x4F56, // 佖
+  0xFA6F: 0x4F92, // 侒
+  0xFA70: 0x4F8A, // 侊
+  0xFA71: 0x4F9A, // 侚
+  0xFA72: 0x4F94, // 侔
+  0xFA73: 0x4FCD, // 俍
+  0xFA74: 0x5040, // 偀
+  0xFA75: 0x5022, // 倢
+  0xFA76: 0x4FFF, // 俿
+  0xFA77: 0x501E, // 倞
+  0xFA78: 0x5046, // 偆
+  0xFA79: 0x5070, // 偰
+  0xFA7A: 0x5042, // 偂
+  0xFA7B: 0x5094, // 傔
+  0xFA7C: 0x50F4, // 僴
+  0xFA7D: 0x50D8, // 僘
+  0xFA7E: 0x514A, // 兊
+  0xFA80: 0x5164, // 兤
+  0xFA81: 0x519D, // 冝
+  0xFA82: 0x51BE, // 冾
+  0xFA83: 0x51EC, // 凬
+  0xFA84: 0x5215, // 刕
+  0xFA85: 0x529C, // 劜
+  0xFA86: 0x52A6, // 劦
+  0xFA87: 0x52C0, // 勀
+  0xFA88: 0x52DB, // 勛
+  0xFA89: 0x5300, // 匀
+  0xFA8A: 0x5307, // 匇
+  0xFA8B: 0x5324, // 匤
+  0xFA8C: 0x5372, // 卲
+  0xFA8D: 0x5393, // 厓
+  0xFA8E: 0x53B2, // 厲
+  0xFA8F: 0x53DD, // 叝
+  0xFA90: 0xFA0E, // 﨎
+  0xFA91: 0x549C, // 咜
+  0xFA92: 0x548A, // 咊
+  0xFA93: 0x54A9, // 咩
+  0xFA94: 0x54FF, // 哿
+  0xFA95: 0x5586, // 喆
+  0xFA96: 0x5759, // 坙
+  0xFA97: 0x5765, // 坥
+  0xFA98: 0x57AC, // 垬
+  0xFA99: 0x57C8, // 埈
+  0xFA9A: 0x57C7, // 埇
+  0xFA9B: 0xFA0F, // 﨏
+  0xFA9C: 0xFA10, // 塚
+  0xFA9D: 0x589E, // 增
+  0xFA9E: 0x58B2, // 墲
+  0xFA9F: 0x590B, // 夋
+  0xFAA0: 0x5953, // 奓
+  0xFAA1: 0x595B, // 奛
+  0xFAA2: 0x595D, // 奝
+  0xFAA3: 0x5963, // 奣
+  0xFAA4: 0x59A4, // 妤
+  0xFAA5: 0x59BA, // 妺
+  0xFAA6: 0x5B56, // 孖
+  0xFAA7: 0x5BC0, // 寀
+  0xFAA8: 0x752F, // 甯
+  0xFAA9: 0x5BD8, // 寘
+  0xFAAA: 0x5BEC, // 寬
+  0xFAAB: 0x5C1E, // 尞
+  0xFAAC: 0x5CA6, // 岦
+  0xFAAD: 0x5CBA, // 岺
+  0xFAAE: 0x5CF5, // 峵
+  0xFAAF: 0x5D27, // 崧
+  0xFAB0: 0x5D53, // 嵓
+  0xFAB1: 0xFA11, // 﨑
+  0xFAB2: 0x5D42, // 嵂
+  0xFAB3: 0x5D6D, // 嵭
+  0xFAB4: 0x5DB8, // 嶸
+  0xFAB5: 0x5DB9, // 嶹
+  0xFAB6: 0x5DD0, // 巐
+  0xFAB7: 0x5F21, // 弡
+  0xFAB8: 0x5F34, // 弴
+  0xFAB9: 0x5F67, // 彧
+  0xFABA: 0x5FB7, // 德
+  0xFABB: 0x5FDE, // 忞
+  0xFABC: 0x605D, // 恝
+  0xFABD: 0x6085, // 悅
+  0xFABE: 0x608A, // 悊
+  0xFABF: 0x60DE, // 惞
+  0xFAC0: 0x60D5, // 惕
+  0xFAC1: 0x6120, // 愠
+  0xFAC2: 0x60F2, // 惲
+  0xFAC3: 0x6111, // 愑
+  0xFAC4: 0x6137, // 愷
+  0xFAC5: 0x6130, // 愰
+  0xFAC6: 0x6198, // 憘
+  0xFAC7: 0x6213, // 戓
+  0xFAC8: 0x62A6, // 抦
+  0xFAC9: 0x63F5, // 揵
+  0xFACA: 0x6460, // 摠
+  0xFACB: 0x649D, // 撝
+  0xFACC: 0x64CE, // 擎
+  0xFACD: 0x654E, // 敎
+  0xFACE: 0x6600, // 昀
+  0xFACF: 0x6615, // 昕
+  0xFAD0: 0x663B, // 昻
+  0xFAD1: 0x6609, // 昉
+  0xFAD2: 0x662E, // 昮
+  0xFAD3: 0x661E, // 昞
+  0xFAD4: 0x6624, // 昤
+  0xFAD5: 0x6665, // 晥
+  0xFAD6: 0x6657, // 晗
+  0xFAD7: 0x6659, // 晙
+  0xFAD8: 0xFA12, // 晴
+  0xFAD9: 0x6673, // 晳
+  0xFADA: 0x6699, // 暙
+  0xFADB: 0x66A0, // 暠
+  0xFADC: 0x66B2, // 暲
+  0xFADD: 0x66BF, // 暿
+  0xFADE: 0x66FA, // 曺
+  0xFADF: 0x670E, // 朎
+  0xFAE0: 0xF929, // 朗
+  0xFAE1: 0x6766, // 杦
+  0xFAE2: 0x67BB, // 枻
+  0xFAE3: 0x6852, // 桒
+  0xFAE4: 0x67C0, // 柀
+  0xFAE5: 0x6801, // 栁
+  0xFAE6: 0x6844, // 桄
+  0xFAE7: 0x68CF, // 棏
+  0xFAE8: 0xFA13, // 﨓
+  0xFAE9: 0x6968, // 楨
+  0xFAEA: 0xFA14, // 﨔
+  0xFAEB: 0x6998, // 榘
+  0xFAEC: 0x69E2, // 槢
+  0xFAED: 0x6A30, // 樰
+  0xFAEE: 0x6A6B, // 橫
+  0xFAEF: 0x6A46, // 橆
+  0xFAF0: 0x6A73, // 橳
+  0xFAF1: 0x6A7E, // 橾
+  0xFAF2: 0x6AE2, // 櫢
+  0xFAF3: 0x6AE4, // 櫤
+  0xFAF4: 0x6BD6, // 毖
+  0xFAF5: 0x6C3F, // 氿
+  0xFAF6: 0x6C5C, // 汜
+  0xFAF7: 0x6C86, // 沆
+  0xFAF8: 0x6C6F, // 汯
+  0xFAF9: 0x6CDA, // 泚
+  0xFAFA: 0x6D04, // 洄
+  0xFAFB: 0x6D87, // 涇
+  0xFAFC: 0x6D6F, // 浯
+  0xFB40: 0x6D96, // 涖
+  0xFB41: 0x6DAC, // 涬
+  0xFB42: 0x6DCF, // 淏
+  0xFB43: 0x6DF8, // 淸
+  0xFB44: 0x6DF2, // 淲
+  0xFB45: 0x6DFC, // 淼
+  0xFB46: 0x6E39, // 渹
+  0xFB47: 0x6E5C, // 湜
+  0xFB48: 0x6E27, // 渧
+  0xFB49: 0x6E3C, // 渼
+  0xFB4A: 0x6EBF, // 溿
+  0xFB4B: 0x6F88, // 澈
+  0xFB4C: 0x6FB5, // 澵
+  0xFB4D: 0x6FF5, // 濵
+  0xFB4E: 0x7005, // 瀅
+  0xFB4F: 0x7007, // 瀇
+  0xFB50: 0x7028, // 瀨
+  0xFB51: 0x7085, // 炅
+  0xFB52: 0x70AB, // 炫
+  0xFB53: 0x710F, // 焏
+  0xFB54: 0x7104, // 焄
+  0xFB55: 0x715C, // 煜
+  0xFB56: 0x7146, // 煆
+  0xFB57: 0x7147, // 煇
+  0xFB58: 0xFA15, // 凞
+  0xFB59: 0x71C1, // 燁
+  0xFB5A: 0x71FE, // 燾
+  0xFB5B: 0x72B1, // 犱
+  0xFB5C: 0x72BE, // 犾
+  0xFB5D: 0x7324, // 猤
+  0xFB5E: 0xFA16, // 猪
+  0xFB5F: 0x7377, // 獷
+  0xFB60: 0x73BD, // 玽
+  0xFB61: 0x73C9, // 珉
+  0xFB62: 0x73D6, // 珖
+  0xFB63: 0x73E3, // 珣
+  0xFB64: 0x73D2, // 珒
+  0xFB65: 0x7407, // 琇
+  0xFB66: 0x73F5, // 珵
+  0xFB67: 0x7426, // 琦
+  0xFB68: 0x742A, // 琪
+  0xFB69: 0x7429, // 琩
+  0xFB6A: 0x742E, // 琮
+  0xFB6B: 0x7462, // 瑢
+  0xFB6C: 0x7489, // 璉
+  0xFB6D: 0x749F, // 璟
+  0xFB6E: 0x7501, // 甁
+  0xFB6F: 0x756F, // 畯
+  0xFB70: 0x7682, // 皂
+  0xFB71: 0x769C, // 皜
+  0xFB72: 0x769E, // 皞
+  0xFB73: 0x769B, // 皛
+  0xFB74: 0x76A6, // 皦
+  0xFB75: 0xFA17, // 益
+  0xFB76: 0x7746, // 睆
+  0xFB77: 0x52AF, // 劯
+  0xFB78: 0x7821, // 砡
+  0xFB79: 0x784E, // 硎
+  0xFB7A: 0x7864, // 硤
+  0xFB7B: 0x787A, // 硺
+  0xFB7C: 0x7930, // 礰
+  0xFB7D: 0xFA18, // 礼
+  0xFB7E: 0xFA19, // 神
+  0xFB80: 0xFA1A, // 祥
+  0xFB81: 0x7994, // 禔
+  0xFB82: 0xFA1B, // 福
+  0xFB83: 0x799B, // 禛
+  0xFB84: 0x7AD1, // 竑
+  0xFB85: 0x7AE7, // 竧
+  0xFB86: 0xFA1C, // 靖
+  0xFB87: 0x7AEB, // 竫
+  0xFB88: 0x7B9E, // 箞
+  0xFB89: 0xFA1D, // 精
+  0xFB8A: 0x7D48, // 絈
+  0xFB8B: 0x7D5C, // 絜
+  0xFB8C: 0x7DB7, // 綷
+  0xFB8D: 0x7DA0, // 綠
+  0xFB8E: 0x7DD6, // 緖
+  0xFB8F: 0x7E52, // 繒
+  0xFB90: 0x7F47, // 罇
+  0xFB91: 0x7FA1, // 羡
+  0xFB92: 0xFA1E, // 羽
+  0xFB93: 0x8301, // 茁
+  0xFB94: 0x8362, // 荢
+  0xFB95: 0x837F, // 荿
+  0xFB96: 0x83C7, // 菇
+  0xFB97: 0x83F6, // 菶
+  0xFB98: 0x8448, // 葈
+  0xFB99: 0x84B4, // 蒴
+  0xFB9A: 0x8553, // 蕓
+  0xFB9B: 0x8559, // 蕙
+  0xFB9C: 0x856B, // 蕫
+  0xFB9D: 0xFA1F, // 﨟
+  0xFB9E: 0x85B0, // 薰
+  0xFB9F: 0xFA20, // 蘒
+  0xFBA0: 0xFA21, // 﨡
+  0xFBA1: 0x8807, // 蠇
+  0xFBA2: 0x88F5, // 裵
+  0xFBA3: 0x8A12, // 訒
+  0xFBA4: 0x8A37, // 訷
+  0xFBA5: 0x8A79, // 詹
+  0xFBA6: 0x8AA7, // 誧
+  0xFBA7: 0x8ABE, // 誾
+  0xFBA8: 0x8ADF, // 諟
+  0xFBA9: 0xFA22, // 諸
+  0xFBAA: 0x8AF6, // 諶
+  0xFBAB: 0x8B53, // 譓
+  0xFBAC: 0x8B7F, // 譿
+  0xFBAD: 0x8CF0, // 賰
+  0xFBAE: 0x8CF4, // 賴
+  0xFBAF: 0x8D12, // 贒
+  0xFBB0: 0x8D76, // 赶
+  0xFBB1: 0xFA23, // 﨣
+  0xFBB2: 0x8ECF, // 軏
+  0xFBB3: 0xFA24, // 﨤
+  0xFBB4: 0xFA25, // 逸
+  0xFBB5: 0x9067, // 遧
+  0xFBB6: 0x90DE, // 郞
+  0xFBB7: 0xFA26, // 都
+  0xFBB8: 0x9115, // 鄕
+  0xFBB9: 0x9127, // 鄧
+  0xFBBA: 0x91DA, // 釚
+  0xFBBB: 0x91D7, // 釗
+  0xFBBC: 0x91DE, // 釞
+  0xFBBD: 0x91ED, // 釭
+  0xFBBE: 0x91EE, // 釮
+  0xFBBF: 0x91E4, // 釤
+  0xFBC0: 0x91E5, // 釥
+  0xFBC1: 0x9206, // 鈆
+  0xFBC2: 0x9210, // 鈐
+  0xFBC3: 0x920A, // 鈊
+  0xFBC4: 0x923A, // 鈺
+  0xFBC5: 0x9240, // 鉀
+  0xFBC6: 0x923C, // 鈼
+  0xFBC7: 0x924E, // 鉎
+  0xFBC8: 0x9259, // 鉙
+  0xFBC9: 0x9251, // 鉑
+  0xFBCA: 0x9239, // 鈹
+  0xFBCB: 0x9267, // 鉧
+  0xFBCC: 0x92A7, // 銧
+  0xFBCD: 0x9277, // 鉷
+  0xFBCE: 0x9278, // 鉸
+  0xFBCF: 0x92E7, // 鋧
+  0xFBD0: 0x92D7, // 鋗
+  0xFBD1: 0x92D9, // 鋙
+  0xFBD2: 0x92D0, // 鋐
+  0xFBD3: 0xFA27, // 﨧
+  0xFBD4: 0x92D5, // 鋕
+  0xFBD5: 0x92E0, // 鋠
+  0xFBD6: 0x92D3, // 鋓
+  0xFBD7: 0x9325, // 錥
+  0xFBD8: 0x9321, // 錡
+  0xFBD9: 0x92FB, // 鋻
+  0xFBDA: 0xFA28, // 﨨
+  0xFBDB: 0x931E, // 錞
+  0xFBDC: 0x92FF, // 鋿
+  0xFBDD: 0x931D, // 錝
+  0xFBDE: 0x9302, // 錂
+  0xFBDF: 0x9370, // 鍰
+  0xFBE0: 0x9357, // 鍗
+  0xFBE1: 0x93A4, // 鎤
+  0xFBE2: 0x93C6, // 鏆
+  0xFBE3: 0x93DE, // 鏞
+  0xFBE4: 0x93F8, // 鏸
+  0xFBE5: 0x9431, // 鐱
+  0xFBE6: 0x9445, // 鑅
+  0xFBE7: 0x9448, // 鑈
+  0xFBE8: 0x9592, // 閒
+  0xFBE9: 0xF9DC, // 隆
+  0xFBEA: 0xFA29, // 﨩
+  0xFBEB: 0x969D, // 隝
+  0xFBEC: 0x96AF, // 隯
+  0xFBED: 0x9733, // 霳
+  0xFBEE: 0x973B, // 霻
+  0xFBEF: 0x9743, // 靃
+  0xFBF0: 0x974D, // 靍
+  0xFBF1: 0x974F, // 靏
+  0xFBF2: 0x9751, // 靑
+  0xFBF3: 0x9755, // 靕
+  0xFBF4: 0x9857, // 顗
+  0xFBF5: 0x9865, // 顥
+  0xFBF6: 0xFA2A, // 飯
+  0xFBF7: 0xFA2B, // 飼
+  0xFBF8: 0x9927, // 餧
+  0xFBF9: 0xFA2C, // 館
+  0xFBFA: 0x999E, // 馞
+  0xFBFB: 0x9A4E, // 驎
+  0xFBFC: 0x9AD9, // 髙
+  0xFC40: 0x9ADC, // 髜
+  0xFC41: 0x9B75, // 魵
+  0xFC42: 0x9B72, // 魲
+  0xFC43: 0x9B8F, // 鮏
+  0xFC44: 0x9BB1, // 鮱
+  0xFC45: 0x9BBB, // 鮻
+  0xFC46: 0x9C00, // 鰀
+  0xFC47: 0x9D70, // 鵰
+  0xFC48: 0x9D6B, // 鵫
+  0xFC49: 0xFA2D, // 鶴
+  0xFC4A: 0x9E19, // 鸙
+  0xFC4B: 0x9ED1 // 黑
+};
diff --git a/tests/cp932-nec-duplicate-map.js b/tests/cp932-nec-duplicate-map.js
new file mode 100644
index 0000000..2b0697c
--- /dev/null
+++ b/tests/cp932-nec-duplicate-map.js
@@ -0,0 +1,26 @@
+/**
+ * Unicode mappings for SJIS (CP932) duplicate codes
+ *
+ * Includes:
+ * - NEC special characters (9 codes in 0x8740 - 0x879C)
+ * - NEC-selected IBM extended characters (0xEEF9)
+ *
+ * Reference:
+ * https://unicode.org/Public/MAPPINGS/VENDORS/MICSFT/WINDOWS/CP932.TXT
+ *
+ * The keys are SJIS codes and the values are Unicode code points.
+ *
+ * { SJIS : UNICODE }
+ */
+module.exports = {
+  0x8790: 0x2252, // ≒ (NEC special characters)
+  0x8791: 0x2261, // ≡
+  0x8792: 0x222B, // ∫
+  0x8795: 0x221A, // √
+  0x8796: 0x22A5, // ⊥
+  0x8797: 0x2220, // ∠
+  0x879A: 0x2235, // ∵
+  0x879B: 0x2229, // ∩
+  0x879C: 0x222A, // ∪
+  0xEEF9: 0xFFE2  // ￢ (NEC-selected IBM extended characters)
+};
diff --git a/tests/test.js b/tests/test.js
index 89aa5ed..34813c8 100644
--- a/tests/test.js
+++ b/tests/test.js
@@ -155,6 +155,79 @@ describe('encoding', function() {
       assert(encoding.detect(utf32le) === 'UTF32');
     });
 
+    it('SJIS detection does not skip leading bytes above 0x80', function() {
+      // "あいう" in UTF-8
+      // All bytes are above 0x80 and should not be skipped before SJIS validation
+      // In encoding.js 2.2.0 and earlier, leading bytes above 0x80 were skipped.
+      var utf8 = [0xE3, 0x81, 0x82, 0xE3, 0x81, 0x84, 0xE3, 0x81, 0x86];
+
+      assert.equal(encoding.detect(utf8, 'SJIS'), false);
+      assert.equal(encoding.detect([0x81], 'SJIS'), false);
+      assert.equal(encoding.detect([0x65E5], 'SJIS'), false);
+    });
+
+    it('SJIS (CP932) extended character areas', function() {
+      var isSJIS = function(data) {
+        return encoding.detect(data, 'SJIS');
+      };
+
+      // NEC special character area (0x8740 - 0x879C)
+      assert.equal(isSJIS([0x87, 0x40]), 'SJIS');
+      assert.equal(isSJIS([0x87, 0x9C]), 'SJIS');
+      // NEC-selected IBM extended character area (0xED40 - 0xEEFC)
+      assert.equal(isSJIS([0xED, 0x40]), 'SJIS');
+      assert.equal(isSJIS([0xEE, 0xFC]), 'SJIS');
+      // User-defined character area (0xF040 - 0xF9FC)
+      assert.equal(isSJIS([0xF0, 0x40]), 'SJIS');
+      assert.equal(isSJIS([0xF9, 0xFC]), 'SJIS');
+      // IBM extended character area (0xFA40 - 0xFC4B)
+      assert.equal(isSJIS([0xFA, 0x40]), 'SJIS');
+      assert.equal(isSJIS([0xFC, 0x4B]), 'SJIS');
+
+      // Check "テスト" followed by the first and last character of each extended area
+      var sjisPrefix = [0x83, 0x65, 0x83, 0x58, 0x83, 0x67]; // "テスト" in SJIS
+
+      // "①" (0x8740) : the first NEC special character
+      assert.equal(encoding.detect(sjisPrefix.concat([0x87, 0x40])), 'SJIS');
+      // "∪" (0x879C) : the last NEC special character
+      assert.equal(encoding.detect(sjisPrefix.concat([0x87, 0x9C])), 'SJIS');
+
+      // the first NEC-selected IBM extended character
+      assert.equal(encoding.detect(sjisPrefix.concat([0xED, 0x40])), 'SJIS');
+      // the last NEC-selected IBM extended character
+      assert.equal(encoding.detect(sjisPrefix.concat([0xEE, 0xFC])), 'SJIS');
+
+      // the first User-defined character
+      assert.equal(encoding.detect(sjisPrefix.concat([0xF0, 0x40])), 'SJIS');
+      // the last User-defined character
+      assert.equal(encoding.detect(sjisPrefix.concat([0xF9, 0xFC])), 'SJIS');
+
+      // the first IBM extended character
+      assert.equal(encoding.detect(sjisPrefix.concat([0xFA, 0x40])), 'SJIS');
+      // the last IBM extended character
+      assert.equal(encoding.detect(sjisPrefix.concat([0xFC, 0x4B])), 'SJIS');
+    });
+
+    it('Invalid SJIS byte sequences', function() {
+      // IBM extended character area ends at 0xFC4B
+      assert.equal(encoding.detect([0xFC, 0x4C], 'SJIS'), false);
+      assert.equal(encoding.detect([0x83, 0x65, 0xFC, 0x4C], 'SJIS'), false);
+      assert.equal(encoding.detect([0x83, 0x65, 0xFC, 0xFC], 'SJIS'), false);
+
+      // Invalid lead bytes
+      assert.equal(encoding.detect([0xA0, 0x40], 'SJIS'), false);
+      assert.equal(encoding.detect([0xFD, 0x40], 'SJIS'), false);
+
+      // Trail bytes outside 0x40 - 0xFC, and 0x7F is not used in SJIS
+      assert.equal(encoding.detect([0x81, 0x3F], 'SJIS'), false);
+      assert.equal(encoding.detect([0x81, 0x7F], 'SJIS'), false);
+      assert.equal(encoding.detect([0x81, 0xFD], 'SJIS'), false);
+
+      // A lead byte that is not followed by a trail byte
+      assert.equal(encoding.detect([0xFA], 'SJIS'), false);
+      assert.equal(encoding.detect([0x83, 0x65, 0x83], 'SJIS'), false);
+    });
+
     it('Specifying multiple encodings', function() {
       var unicode = 'ユニコード';
 
@@ -1053,6 +1126,82 @@ describe('encoding', function() {
     });
   });
 
+  describe('convert CP932 extended characters', function() {
+    var ibmExtTable = require('./cp932-ibm-ext-map');
+    var ibmExtSJIS = [];
+    var ibmExtUnicode = [];
+
+    Object.keys(ibmExtTable).forEach(function(sjis) {
+      sjis = sjis | 0;
+      var unicode = ibmExtTable[sjis] | 0;
+      ibmExtSJIS.push(sjis >> 8, sjis & 0xFF);
+      ibmExtUnicode.push(unicode);
+    });
+
+    it('SJIS to UNICODE', function() {
+      var sjis = encoding.convert(ibmExtSJIS, {
+        to: 'unicode',
+        from: 'sjis'
+      });
+      assert.deepEqual(sjis, ibmExtUnicode);
+    });
+
+    it('SJIS to UTF-8', function() {
+      var utf8 = encoding.convert(ibmExtSJIS, {
+        to: 'utf-8',
+        from: 'sjis'
+      });
+      var res = encoding.convert(utf8, {
+        to: 'unicode',
+        from: 'utf-8'
+      });
+      assert.deepEqual(res, ibmExtUnicode);
+    });
+
+    it('SJIS to EUC-JP', function() {
+      var eucjp = encoding.convert(ibmExtSJIS, {
+        to: 'euc-jp',
+        from: 'sjis'
+      });
+      var res = encoding.convert(eucjp, {
+        to: 'unicode',
+        from: 'euc-jp'
+      });
+      assert.deepEqual(res, ibmExtUnicode);
+    });
+
+    it('SJIS to JIS', function() {
+      var jis = encoding.convert(ibmExtSJIS, {
+        to: 'jis',
+        from: 'sjis'
+      });
+      var res = encoding.convert(jis, {
+        to: 'unicode',
+        from: 'jis'
+      });
+      assert.deepEqual(res, ibmExtUnicode);
+    });
+
+    describe('convert CP932 NEC duplicate codes', function() {
+      var cp932NECDuplicateMap = require('./cp932-nec-duplicate-map');
+
+      it('SJIS to UNICODE', function() {
+        Object.keys(cp932NECDuplicateMap).forEach(function(sjis) {
+          sjis = sjis | 0;
+          var unicode = cp932NECDuplicateMap[sjis];
+          var bytes = [sjis >> 8, sjis & 0xFF];
+
+          var res = encoding.convert(bytes, { to: 'unicode', from: 'sjis' });
+          assert.deepEqual(
+            res,
+            [unicode],
+            '0x' + sjis.toString(16).toUpperCase()
+          );
+        });
+      });
+    });
+  });
+
   describe('urlEncode/urlDecode', function() {
     encodings.forEach(function(encodingName) {
       it(encodingName, function () {