diff --git a/src/CommandFormats.hh b/src/CommandFormats.hh
index ca8874e2..2c65aeef 100644
--- a/src/CommandFormats.hh
+++ b/src/CommandFormats.hh
@@ -4780,16 +4780,25 @@ struct G_SyncSetFlagState_6x6E_Decompressed {
 
 // 6x6F: Set quest flags (used while loading into game)
 
-struct G_SetQuestFlagsV1_6x6F {
+struct G_SetQuestFlags_DCv1_6x6F {
   G_UnusedHeader header;
   QuestFlagsV1 quest_flags;
 } __packed__;
 
-struct G_SetQuestFlagsV2V3V4_6x6F {
+struct G_SetQuestFlags_V2_V3_6x6F {
   G_UnusedHeader header;
   QuestFlags quest_flags;
 } __packed__;
 
+struct G_SetQuestFlags_BB_6x6F {
+  G_UnusedHeader header;
+  QuestFlags quest_flags;
+  // If use_apply_mask is 1, only the flags set in bb_quest_flag_apply_mask
+  // (in PlayerSubordinates.cc) are overwritten on the receiving client's end.
+  // The client always sends this with use_apply_mask = 1.
+  le_uint32_t use_apply_mask = 1;
+} __packed__;
+
 // 6x70: Sync player disp data and inventory (used while loading into game)
 // Annoyingly, they didn't use the same format as the 65/67/68 commands here,
 // and instead rearranged a bunch of things.
diff --git a/src/PlayerSubordinates.cc b/src/PlayerSubordinates.cc
index 43f0a998..81b5bc44 100644
--- a/src/PlayerSubordinates.cc
+++ b/src/PlayerSubordinates.cc
@@ -1114,3 +1114,47 @@ string RecentSwitchFlags::enable_commands(uint8_t floor) const {
   }
   return std::move(w.str());
 }
+
+const QuestFlagsForDifficulty bb_quest_flag_apply_mask{{
+    // clang-format off
+    /* 0000 */ 0x00, 0x3F, 0xFF, 0xE3, 0xE0, 0xFF, 0xFF, 0x00,
+    /* 0040 */ 0x03, 0xFF, 0xFF, 0xFF, 0xF0, 0x00, 0x00, 0x00,
+    /* 0080 */ 0x00, 0x00, 0x01, 0xE0, 0x00, 0x00, 0x00, 0x00,
+    /* 00C0 */ 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00,
+    /* 0100 */ 0x00, 0x00, 0x00, 0x00, 0x00, 0x07, 0xFC, 0x00,
+    /* 0140 */ 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF,
+    /* 0180 */ 0xFE, 0x00, 0x7F, 0xFE, 0x0F, 0xFF, 0xFF, 0x80,
+    /* 01C0 */ 0x3F, 0xFF, 0xFE, 0x00, 0x00, 0x00, 0x0F, 0xFF,
+    /* 0200 */ 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFC, 0x00,
+    /* 0240 */ 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00,
+    /* 0280 */ 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x07,
+    /* 02C0 */ 0xF8, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00,
+    /* 0300 */ 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00,
+    /* 0340 */ 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00,
+    /* 0380 */ 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00,
+    /* 03C0 */ 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00,
+    // clang-format on
+
+    // The flags in the above mask are:
+    // 000A 000B 000C 000D 000E 000F 0010 0011 0012 0013 0014 0015 0016 0017
+    // 0018 0019 001A 001E 001F 0020 0021 0022 0028 0029 002A 002B 002C 002D
+    // 002E 002F 0030 0031 0032 0033 0034 0035 0036 0037 0046 0047 0048 0049
+    // 004A 004B 004C 004D 004E 004F 0050 0051 0052 0053 0054 0055 0056 0057
+    // 0058 0059 005A 005B 005C 005D 005E 005F 0060 0061 0062 0063 0097 0098
+    // 0099 009A 012D 012E 012F 0130 0131 0132 0133 0134 0135 0140 0141 0142
+    // 0143 0144 0145 0146 0147 0148 0149 014A 014B 014C 014D 014E 014F 0150
+    // 0151 0152 0153 0154 0155 0156 0157 0158 0159 015A 015B 015C 015D 015E
+    // 015F 0160 0161 0162 0163 0164 0165 0166 0167 0168 0169 016A 016B 016C
+    // 016D 016E 016F 0170 0171 0172 0173 0174 0175 0176 0177 0178 0179 017A
+    // 017B 017C 017D 017E 017F 0180 0181 0182 0183 0184 0185 0186 0191 0192
+    // 0193 0194 0195 0196 0197 0198 0199 019A 019B 019C 019D 019E 01A4 01A5
+    // 01A6 01A7 01A8 01A9 01AA 01AB 01AC 01AD 01AE 01AF 01B0 01B1 01B2 01B3
+    // 01B4 01B5 01B6 01B7 01B8 01C2 01C3 01C4 01C5 01C6 01C7 01C8 01C9 01CA
+    // 01CB 01CC 01CD 01CE 01CF 01D0 01D1 01D2 01D3 01D4 01D5 01D6 01F4 01F5
+    // 01F6 01F7 01F8 01F9 01FA 01FB 01FC 01FD 01FE 01FF 0200 0201 0202 0203
+    // 0204 0205 0206 0207 0208 0209 020A 020B 020C 020D 020E 020F 0210 0211
+    // 0212 0213 0214 0215 0216 0217 0218 0219 021A 021B 021C 021D 021E 021F
+    // 0220 0221 0222 0223 0224 0225 0226 0227 0228 0229 022A 022B 022C 022D
+    // 022E 022F 0230 0231 0232 0233 0234 0235 02BD 02BE 02BF 02C0 02C1 02C2
+    // 02C3 02C4
+}};
diff --git a/src/PlayerSubordinates.hh b/src/PlayerSubordinates.hh
index 1b82b5d6..489fa63b 100644
--- a/src/PlayerSubordinates.hh
+++ b/src/PlayerSubordinates.hh
@@ -745,3 +745,5 @@ struct RecentSwitchFlags {
 
   std::string enable_commands(uint8_t floor) const;
 };
+
+extern const QuestFlagsForDifficulty bb_quest_flag_apply_mask;
diff --git a/src/ReceiveSubcommands.cc b/src/ReceiveSubcommands.cc
index c6e7e911..3a82eaa1 100644
--- a/src/ReceiveSubcommands.cc
+++ b/src/ReceiveSubcommands.cc
@@ -644,9 +644,11 @@ static void on_sync_joining_player_quest_flags_t(shared_ptr<Client> c, uint8_t c
 
 static void on_sync_joining_player_quest_flags(shared_ptr<Client> c, uint8_t command, uint8_t flag, void* data, size_t size) {
   if (is_v1(c->version())) {
-    on_sync_joining_player_quest_flags_t<G_SetQuestFlagsV1_6x6F>(c, command, flag, data, size);
+    on_sync_joining_player_quest_flags_t<G_SetQuestFlags_DCv1_6x6F>(c, command, flag, data, size);
+  } else if (!is_v4(c->version())) {
+    on_sync_joining_player_quest_flags_t<G_SetQuestFlags_V2_V3_6x6F>(c, command, flag, data, size);
   } else {
-    on_sync_joining_player_quest_flags_t<G_SetQuestFlagsV2V3V4_6x6F>(c, command, flag, data, size);
+    on_sync_joining_player_quest_flags_t<G_SetQuestFlags_BB_6x6F>(c, command, flag, data, size);
   }
 }
 
diff --git a/src/SendCommands.cc b/src/SendCommands.cc
index fc1fb1a2..950d715e 100644
--- a/src/SendCommands.cc
+++ b/src/SendCommands.cc
@@ -2709,10 +2709,14 @@ void send_game_flag_state_t(shared_ptr<Client> c) {
 void send_game_flag_state(shared_ptr<Client> c) {
   // DC NTE and 11/2000 don't have this command at all; v1 has it but it doesn't
   // include flags for Ultimate.
-  if (!is_v1(c->version())) {
-    send_game_flag_state_t<G_SetQuestFlagsV2V3V4_6x6F>(c);
-  } else if (!is_pre_v1(c->version())) {
-    send_game_flag_state_t<G_SetQuestFlagsV1_6x6F>(c);
+  if (is_pre_v1(c->version())) {
+    return;
+  } else if (is_v1(c->version())) {
+    send_game_flag_state_t<G_SetQuestFlags_DCv1_6x6F>(c);
+  } else if (!is_v4(c->version())) {
+    send_game_flag_state_t<G_SetQuestFlags_V2_V3_6x6F>(c);
+  } else {
+    send_game_flag_state_t<G_SetQuestFlags_BB_6x6F>(c);
   }
 }