diff --git a/src/auth/auth_packets.cpp b/src/auth/auth_packets.cpp
index c8f74f59..6f99c31f 100644
--- a/src/auth/auth_packets.cpp
+++ b/src/auth/auth_packets.cpp
@@ -25,13 +25,14 @@ network::Packet LogonChallengePacket::build(const std::string& account, const Cl
     // Payload size
     packet.writeUInt16(payloadSize);
 
-    // Write a 4-byte ASCII field (FourCC-ish): bytes are sent in-order and null-padded.
-    // Auth servers expect literal "x86\0", "Win\0", "enUS", etc (not reversed).
-    auto writeFourCC = [&packet](const std::string& str) {
+    // Write a FourCC-like 4-byte ASCII field in the legacy login wire format:
+    // reverse the characters and null-pad to 4 bytes.
+    // Example (1.12.1): platform "x86" is sent as bytes "68x\\0"; os "Win" as "niW\\0"; locale "enGB" as "BGne".
+    auto writeFourCCLE = [&packet](const std::string& str) {
         uint8_t buf[4] = {0, 0, 0, 0};
         size_t len = std::min<size_t>(4, str.length());
         for (size_t i = 0; i < len; ++i) {
-            buf[i] = static_cast<uint8_t>(str[i]);
+            buf[i] = static_cast<uint8_t>(str[len - 1 - i]);
         }
         for (int i = 0; i < 4; ++i) {
             packet.writeUInt8(buf[i]);
@@ -58,14 +59,14 @@ network::Packet LogonChallengePacket::build(const std::string& account, const Cl
     // Build (2 bytes)
     packet.writeUInt16(info.build);
 
-    // Platform (4 bytes)
-    writeFourCC(info.platform);
+    // Platform (4 bytes, legacy reversed encoding)
+    writeFourCCLE(info.platform);
 
-    // OS (4 bytes)
-    writeFourCC(info.os);
+    // OS (4 bytes, legacy reversed encoding)
+    writeFourCCLE(info.os);
 
-    // Locale (4 bytes)
-    writeFourCC(info.locale);
+    // Locale (4 bytes, legacy reversed encoding)
+    writeFourCCLE(info.locale);
 
     // Timezone
     packet.writeUInt32(info.timezone);