diff --git a/src/Compression.cc b/src/Compression.cc
index a7eeda70..91a23ab9 100644
--- a/src/Compression.cc
+++ b/src/Compression.cc
@@ -96,10 +96,11 @@ struct prs_compress_ctx {
   }
 };
 
-string prs_compress(const string& data) {
+string prs_compress(const void* vdata, size_t size) {
+  const uint8_t* data = reinterpret_cast<const uint8_t*>(vdata);
   prs_compress_ctx pc;
 
-  ssize_t data_ssize = static_cast<ssize_t>(data.size());
+  ssize_t data_ssize = static_cast<ssize_t>(size);
   ssize_t read_offset = 0;
   while (read_offset < data_ssize) {
 
@@ -117,8 +118,8 @@ string prs_compress(const string& data) {
       while ((this_size < 0x100) && // max copy size is 255 bytes
              ((this_offset + this_size) < 0) && // don't copy past the read offset
              (this_size <= data_ssize - read_offset) && // don't copy past the end
-             !memcmp(data.data() + read_offset + this_offset,
-                     data.data() + read_offset, this_size)) {
+             !memcmp(data + read_offset + this_offset, data + read_offset,
+                     this_size)) {
         this_size++;
       }
       this_size--;
@@ -143,6 +144,10 @@ string prs_compress(const string& data) {
   return pc.finish();
 }
 
+string prs_compress(const string& data) {
+  return prs_compress(data.data(), data.size());
+}
+
 
 
 static int16_t get_u8_or_eof(StringReader& r) {
diff --git a/src/Compression.hh b/src/Compression.hh
index 7b59bcf1..726600bc 100644
--- a/src/Compression.hh
+++ b/src/Compression.hh
@@ -6,6 +6,8 @@
 
 
 
+std::string prs_compress(const void* vdata, size_t size);
 std::string prs_compress(const std::string& data);
+
 std::string prs_decompress(const std::string& data, size_t max_size = 0);
 size_t prs_decompress_size(const std::string& data, size_t max_size = 0);
diff --git a/src/Episode3.cc b/src/Episode3.cc
index 7508a904..d1d26754 100644
--- a/src/Episode3.cc
+++ b/src/Episode3.cc
@@ -774,36 +774,51 @@ Ep3DataIndex::Ep3DataIndex(const string& directory) {
   }
 
   for (const auto& filename : list_directory(directory)) {
-    if (ends_with(filename, ".mnm")) {
-      try {
-        string compressed_data = load_file(directory + "/" + filename);
-        // There's a small header (Ep3CompressedMapHeader) before the compressed
-        // data, which we ignore
-        string data_to_decompress = compressed_data.substr(8);
-        string data = prs_decompress(data_to_decompress);
-        if (data.size() != sizeof(Ep3Map)) {
-          throw runtime_error(string_printf(
-              "decompressed data size is incorrect (expected %zu bytes, read %zu bytes)",
-              sizeof(Ep3Map), data.size()));
-        }
+    try {
+      shared_ptr<MapEntry> entry;
 
-        shared_ptr<MapEntry> entry(new MapEntry(
-            {*reinterpret_cast<const Ep3Map*>(data.data()), move(compressed_data)}));
+      if (ends_with(filename, ".mnmd")) {
+        entry.reset(new MapEntry(load_object_file<Ep3Map>(directory + "/" + filename)));
+      } else if (ends_with(filename, ".mnm")) {
+        entry.reset(new MapEntry(load_file(directory + "/" + filename)));
+      }
+
+      if (entry.get()) {
         if (!this->maps.emplace(entry->map.map_number, entry).second) {
           throw runtime_error("duplicate map number");
         }
         string name = entry->map.name;
         log(INFO, "Indexed Episode 3 map %s (%08" PRIX32 "; %s)",
             filename.c_str(), entry->map.map_number.load(), name.c_str());
-
-      } catch (const exception& e) {
-        log(WARNING, "Failed to index Episode 3 map %s: %s",
-            filename.c_str(), e.what());
       }
+
+    } catch (const exception& e) {
+      log(WARNING, "Failed to index Episode 3 map %s: %s",
+          filename.c_str(), e.what());
     }
   }
 }
 
+Ep3DataIndex::MapEntry::MapEntry(const Ep3Map& map) : map(map) { }
+
+Ep3DataIndex::MapEntry::MapEntry(const string& compressed)
+  : compressed_data(compressed) {
+  string decompressed = prs_decompress(this->compressed_data);
+  if (decompressed.size() != sizeof(Ep3Map)) {
+    throw runtime_error(string_printf(
+        "decompressed data size is incorrect (expected %zu bytes, read %zu bytes)",
+        sizeof(Ep3Map), decompressed.size()));
+  }
+  this->map = *reinterpret_cast<const Ep3Map*>(decompressed.data());
+}
+
+string Ep3DataIndex::MapEntry::compressed() const {
+  if (this->compressed_data.empty()) {
+    this->compressed_data = prs_compress(&this->map, sizeof(this->map));
+  }
+  return this->compressed_data;
+}
+
 const string& Ep3DataIndex::get_compressed_card_definitions() const {
   if (this->compressed_card_definitions.empty()) {
     throw runtime_error("card definitions are not available");
diff --git a/src/Episode3.hh b/src/Episode3.hh
index f05d00a7..db8e2639 100644
--- a/src/Episode3.hh
+++ b/src/Episode3.hh
@@ -295,7 +295,7 @@ struct Ep3Map { // .mnm format (after decompressing and discarding the header)
     ptext<char, 0x10> name;
     parray<be_uint16_t, 0x7E> unknown_a3;
   } __attribute__((packed));
-  /* 20F0 */ parray<NPCCharacter, 3> npc_chars; // Unused if name[0] == 0
+  /* 20F0 */ NPCCharacter npc_chars[3]; // Unused if name[0] == 0
   /* 242C */ parray<uint8_t, 0x14> unknown_a8; // Always FF?
   /* 2440 */ ptext<char, 0x190> before_message;
   /* 25D0 */ ptext<char, 0x190> after_message;
@@ -305,7 +305,7 @@ struct Ep3Map { // .mnm format (after decompressing and discarding the header)
     be_uint16_t unknown_a2; // Always 0x0064 if valid, 0xFFFF if unused?
     ptext<char, 0x40> strings[4];
   } __attribute__((packed)); // Total size: 0x104 bytes
-  /* 28F0 */ parray<DialogueSet, 0x10> dialogue_sets[3]; // Up to 0x10 per valid NPC
+  /* 28F0 */ DialogueSet dialogue_sets[3][0x10]; // Up to 0x10 per valid NPC
   /* 59B0 */ be_uint16_t reward_card_id; // TODO: This could be an array. The only examples I've seen have only one here
   /* 59B2 */ parray<be_uint16_t, 0x33> unknown_a9;
   /* 5A18 */
@@ -320,9 +320,17 @@ public:
     std::vector<std::string> text;
   };
 
-  struct MapEntry {
+  class MapEntry {
+  public:
     Ep3Map map;
-    std::string compressed_data;
+
+    MapEntry(const Ep3Map& map);
+    MapEntry(const std::string& compressed_data);
+
+    std::string compressed() const;
+
+  private:
+    mutable std::string compressed_data;
   };
 
   const std::string& get_compressed_card_definitions() const;
diff --git a/src/ProxyCommands.cc b/src/ProxyCommands.cc
index 891031b6..aeee7540 100644
--- a/src/ProxyCommands.cc
+++ b/src/ProxyCommands.cc
@@ -26,6 +26,7 @@
 #include <resource_file/Emulators/PPC32Emulator.hh>
 #endif
 
+#include "Compression.hh"
 #include "PSOProtocol.hh"
 #include "SendCommands.hh"
 #include "ReceiveCommands.hh"
@@ -637,11 +638,11 @@ static bool process_server_60_62_6C_6D_C9_CB(shared_ptr<ServerState>,
     if ((session.version == GameVersion::GC) && (data.size() >= 0x14)) {
       PSOSubcommand* subs = &check_size_t<PSOSubcommand>(data, 0x14, 0xFFFF);
       if (subs[0].dword == 0x000000B6 && subs[2].dword == 0x00000041) {
-        string filename = string_printf("map%08" PRIX32 ".%" PRIu64 ".mnm",
+        string filename = string_printf("map%08" PRIX32 ".%" PRIu64 ".mnmd",
             subs[3].dword.load(), now());
-        string file_data = data.substr(0x0C);
-        save_file(filename, file_data);
-        session.log(INFO, "Wrote %zu bytes to %s", file_data.size(), filename.c_str());
+        string map_data = prs_decompress(data.substr(0x14));
+        save_file(filename, map_data);
+        session.log(INFO, "Wrote %zu bytes to %s", map_data.size(), filename.c_str());
       }
     }
   }
diff --git a/src/SendCommands.cc b/src/SendCommands.cc
index 3357665d..5e7b9ab8 100644
--- a/src/SendCommands.cc
+++ b/src/SendCommands.cc
@@ -1399,13 +1399,19 @@ void send_ep3_map_list(shared_ptr<ServerState> s, shared_ptr<Lobby> l) {
 // sends the map data for the chosen map to all players in the game
 void send_ep3_map_data(shared_ptr<ServerState> s, shared_ptr<Lobby> l, uint32_t map_id) {
   auto entry = s->ep3_data_index->get_map(map_id);
+  const auto& compressed = entry->compressed();
 
-  string data(12, '\0');
+  string data(0x14, '\0');
   PSOSubcommand* subs = reinterpret_cast<PSOSubcommand*>(data.data());
   subs[0].dword = 0x000000B6;
-  subs[1].dword = (19 + entry->compressed_data.size()) & 0xFFFFFFFC;
+  subs[1].dword = (19 + compressed.size()) & 0xFFFFFFFC;
   subs[2].dword = 0x00000041;
-  data += entry->compressed_data;
+  subs[3].dword = entry->map.map_number.load();
+  subs[4].dword = compressed.size();
+  data += compressed;
+  while (data.size() & 3) {
+    data.push_back('\0');
+  }
 
   send_command(l, 0x6C, 0x00, data);
 }
diff --git a/system/ep3/map00000230.mnm b/system/ep3/map00000230.mnm
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index 17364c2d..00000000
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