diff --git a/include/map.h b/include/map.h
index e804934649..960d5c0405 100644
--- a/include/map.h
+++ b/include/map.h
@@ -192,10 +192,10 @@ typedef struct Enemy {
 typedef struct {
     /* 0x00 */ s32 npcCount;
     /* 0x04 */ StaticNpc* npcs;
-    /* 0x08 */ s32 battleID;
+    /* 0x08 */ FormationID formationID;
 } NpcGroupList[]; // size = 0x0C
 
-#define NPC_GROUP(npcs, battleID) { sizeof(npcs) / sizeof(StaticNpc), &npcs, battleID }
+#define NPC_GROUP(npcs, formationID) { sizeof(npcs) / sizeof(StaticNpc), &npcs, formationID }
 #define NPC_GROUP_LIST_END() { 0, 0, 0 }
 
 Enemy* get_enemy(NpcId npcId);
diff --git a/include/types.h b/include/types.h
index 8686cc3795..ac7a5dcf3d 100644
--- a/include/types.h
+++ b/include/types.h
@@ -10,4 +10,7 @@
 #define UNK_FUN_PTR(name) void(*name)(void)
 #define UNK_ARGS
 
+typedef s32 FormationID;
+#define FORMATION_ID(section, stage, index) (section << 16) + (stage << 8) + index
+
 #endif
diff --git a/src/world/area_kmr/kmr_12/events.c b/src/world/area_kmr/kmr_12/events.c
index bf67e7bb02..6c986d20fa 100644
--- a/src/world/area_kmr/kmr_12/events.c
+++ b/src/world/area_kmr/kmr_12/events.c
@@ -191,7 +191,7 @@ static StaticNpc goomba_npc = {
 };
 
 static NpcGroupList npc_groups = {
-    NPC_GROUP(goomba_npc, 0x00010003),
+    NPC_GROUP(goomba_npc, FORMATION_ID(1, 0, 3)),
     NPC_GROUP_LIST_END(),
 };