diff --git a/include/data.h b/include/data.h
index ffa1a4cba0..4663bae33c 100644
--- a/include/data.h
+++ b/include/data.h
@@ -198,9 +198,16 @@ extern const struct FollowerMsgInfo gFollowerCuriousMessages[];
 extern const struct FollowerMsgInfo gFollowerMusicMessages[];
 extern const struct FollowerMsgInfo gFollowerPoisonedMessages[];
 
+static inline bool8 IsPartnerTrainerId(u16 trainerId)
+{
+    if (trainerId >= TRAINER_PARTNER(PARTNER_NONE) && trainerId < TRAINER_PARTNER(PARTNER_COUNT))
+        return TRUE;
+    return FALSE;
+}
+
 static inline u16 SanitizeTrainerId(u16 trainerId)
 {
-    if (trainerId >= TRAINERS_COUNT)
+    if (trainerId >= TRAINERS_COUNT && !IsPartnerTrainerId(trainerId))
         return TRAINER_NONE;
     return trainerId;
 }
@@ -212,7 +219,10 @@ static inline const struct Trainer *GetTrainerStructFromId(u16 trainerId)
     sanitizedTrainerId = SanitizeTrainerId(trainerId);
     enum DifficultyLevel difficulty = GetTrainerDifficultyLevel(sanitizedTrainerId);
 
-    return &gTrainers[difficulty][sanitizedTrainerId];
+    if (IsPartnerTrainerId(trainerId))
+        return &gBattlePartners[difficulty][sanitizedTrainerId - TRAINER_PARTNER(PARTNER_NONE)];
+    else
+        return &gTrainers[difficulty][sanitizedTrainerId];
 }
 
 static inline const enum TrainerClassID GetTrainerClassFromId(u16 trainerId)
diff --git a/src/battle_ai_main.c b/src/battle_ai_main.c
index a73de7f94e..b6ddd0dc91 100644
--- a/src/battle_ai_main.c
+++ b/src/battle_ai_main.c
@@ -251,7 +251,7 @@ void BattleAI_SetupFlags(void)
     else
     {
         gAiThinkingStruct->aiFlags[B_POSITION_OPPONENT_LEFT] = GetAiFlags(TRAINER_BATTLE_PARAM.opponentA);
-        if (TRAINER_BATTLE_PARAM.opponentB != 0)
+        if (TRAINER_BATTLE_PARAM.opponentB != 0 && TRAINER_BATTLE_PARAM.opponentB != 0xFFFF)
             gAiThinkingStruct->aiFlags[B_POSITION_OPPONENT_RIGHT] = GetAiFlags(TRAINER_BATTLE_PARAM.opponentB);
         else
             gAiThinkingStruct->aiFlags[B_POSITION_OPPONENT_RIGHT] = gAiThinkingStruct->aiFlags[B_POSITION_OPPONENT_LEFT];
@@ -259,7 +259,7 @@ void BattleAI_SetupFlags(void)
 
     if (gBattleTypeFlags & BATTLE_TYPE_INGAME_PARTNER)
     {
-        gAiThinkingStruct->aiFlags[B_POSITION_PLAYER_RIGHT] = GetAiFlags(gPartnerTrainerId - TRAINER_PARTNER(PARTNER_NONE));
+        gAiThinkingStruct->aiFlags[B_POSITION_PLAYER_RIGHT] = GetAiFlags(gPartnerTrainerId);
     }
     else if (IsDoubleBattle() && IsAiVsAiBattle())
     {