diff --git a/include/global.h b/include/global.h
index 0ca226c03..00b08f48f 100644
--- a/include/global.h
+++ b/include/global.h
@@ -134,6 +134,13 @@
 #define NUM_FLAG_BYTES ROUND_BITS_TO_BYTES(FLAGS_COUNT)
 #define NUM_TRENDY_SAYING_BYTES ROUND_BITS_TO_BYTES(NUM_TRENDY_SAYINGS)
 
+// This returns the number of arguments passed to it (up to 8).
+#define NARG_8(...) NARG_8_(_, ##__VA_ARGS__, 8, 7, 6, 5, 4, 3, 2, 1, 0)
+#define NARG_8_(_, a, b, c, d, e, f, g, h, N, ...) N
+
+#define CAT(a, b) CAT_(a, b)
+#define CAT_(a, b) a ## b
+
 // This produces an error at compile-time if expr is zero.
 // It looks like file.c:line: size of array `id' is negative
 #define STATIC_ASSERT(expr, id) typedef char id[(expr) ? 1 : -1];
diff --git a/include/pokemon.h b/include/pokemon.h
index 54b4841f7..f4f6d6989 100644
--- a/include/pokemon.h
+++ b/include/pokemon.h
@@ -436,12 +436,17 @@ void SetMultiuseSpriteTemplateToPokemon(u16 speciesTag, u8 battlerPosition);
 void SetMultiuseSpriteTemplateToTrainerBack(u16 trainerSpriteId, u8 battlerPosition);
 void SetMultiuseSpriteTemplateToTrainerFront(u16 trainerPicId, u8 battlerPosition);
 
-// These are full type signatures for GetMonData() and GetBoxMonData(),
-// but they are not used since some code erroneously omits the third arg.
-// u32 GetMonData(struct Pokemon *mon, s32 field, u8 *data);
-// u32 GetBoxMonData(struct BoxPokemon *boxMon, s32 field, u8 *data);
-u32 GetMonData();
-u32 GetBoxMonData();
+/* GameFreak called Get(Box)MonData with either 2 or 3 arguments, for
+ * type safety we have a Get(Box)MonData macro which dispatches to
+ * either Get(Box)MonData2 or Get(Box)MonData3 based on the number of
+ * arguments. The two functions are aliases of each other, but they
+ * differ for matching purposes in the caller's codegen. */
+#define GetMonData(...) CAT(GetMonData, NARG_8(__VA_ARGS__))(__VA_ARGS__)
+#define GetBoxMonData(...) CAT(GetBoxMonData, NARG_8(__VA_ARGS__))(__VA_ARGS__)
+u32 GetMonData3(struct Pokemon *mon, s32 field, u8 *data);
+u32 GetMonData2(struct Pokemon *mon, s32 field);
+u32 GetBoxMonData3(struct BoxPokemon *boxMon, s32 field, u8 *data);
+u32 GetBoxMonData2(struct BoxPokemon *boxMon, s32 field);
 
 void SetMonData(struct Pokemon *mon, s32 field, const void *dataArg);
 void SetBoxMonData(struct BoxPokemon *boxMon, s32 field, const void *dataArg);
diff --git a/src/daycare.c b/src/daycare.c
index c3f4dd990..9d199f0f3 100644
--- a/src/daycare.c
+++ b/src/daycare.c
@@ -341,7 +341,7 @@ static void Debug_AddDaycareSteps(u16 numSteps)
 
 u8 GetNumLevelsGainedFromDaycare(void)
 {
-    if (GetBoxMonData(&gSaveBlock1Ptr->daycare.mons[gSpecialVar_0x8004], MON_DATA_SPECIES) != 0)
+    if (GetBoxMonData(&gSaveBlock1Ptr->daycare.mons[gSpecialVar_0x8004].mon, MON_DATA_SPECIES) != 0)
         return GetNumLevelsGainedForDaycareMon(&gSaveBlock1Ptr->daycare.mons[gSpecialVar_0x8004]);
 
     return 0;
diff --git a/src/pokemon.c b/src/pokemon.c
index fa2eee42c..b8f7ae48b 100644
--- a/src/pokemon.c
+++ b/src/pokemon.c
@@ -3622,7 +3622,11 @@ static union PokemonSubstruct *GetSubstruct(struct BoxPokemon *boxMon, u32 perso
     return substruct;
 }
 
-u32 GetMonData(struct Pokemon *mon, s32 field, u8 *data)
+/* GameFreak called GetMonData with either 2 or 3 arguments, for type
+ * safety we have a GetMonData macro (in include/pokemon.h) which
+ * dispatches to either GetMonData2 or GetMonData3 based on the number
+ * of arguments. */
+u32 GetMonData3(struct Pokemon *mon, s32 field, u8 *data)
 {
     u32 ret;
 
@@ -3690,7 +3694,13 @@ u32 GetMonData(struct Pokemon *mon, s32 field, u8 *data)
     return ret;
 }
 
-u32 GetBoxMonData(struct BoxPokemon *boxMon, s32 field, u8 *data)
+u32 GetMonData2(struct Pokemon *mon, s32 field) __attribute__((alias("GetMonData3")));
+
+/* GameFreak called GetBoxMonData with either 2 or 3 arguments, for type
+ * safety we have a GetBoxMonData macro (in include/pokemon.h) which
+ * dispatches to either GetBoxMonData2 or GetBoxMonData3 based on the
+ * number of arguments. */
+u32 GetBoxMonData3(struct BoxPokemon *boxMon, s32 field, u8 *data)
 {
     s32 i;
     u32 retVal = 0;
@@ -4046,6 +4056,8 @@ u32 GetBoxMonData(struct BoxPokemon *boxMon, s32 field, u8 *data)
     return retVal;
 }
 
+u32 GetBoxMonData2(struct BoxPokemon *boxMon, s32 field) __attribute__((alias("GetBoxMonData3")));
+
 #define SET8(lhs) (lhs) = *data
 #define SET16(lhs) (lhs) = data[0] + (data[1] << 8)
 #define SET32(lhs) (lhs) = data[0] + (data[1] << 8) + (data[2] << 16) + (data[3] << 24)