diff --git a/src/battle_main.c b/src/battle_main.c
index 037d9a857..514b69fd6 100644
--- a/src/battle_main.c
+++ b/src/battle_main.c
@@ -1896,7 +1896,7 @@ static u32 GeneratePartyHash(const struct Trainer *trainer, u32 i)
 void ModifyPersonalityForNature(u32 *personality, u32 newNature)
 {
     u32 nature = GetNatureFromPersonality(*personality);
-    s32 diff = abs(nature - newNature);
+    s32 diff = abs((s32)nature - (s32)newNature);
     s32 sign = (nature > newNature) ? 1 : -1;
     if (diff > NUM_NATURES / 2)
     {
diff --git a/test/battle/trainer_control.c b/test/battle/trainer_control.c
index a0e94dbbe..99bea0e8c 100644
--- a/test/battle/trainer_control.c
+++ b/test/battle/trainer_control.c
@@ -4,6 +4,7 @@
 #include "battle_main.h"
 #include "data.h"
 #include "malloc.h"
+#include "random.h"
 #include "string_util.h"
 #include "constants/item.h"
 #include "constants/abilities.h"
@@ -119,3 +120,17 @@ TEST("CreateNPCTrainerPartyForTrainer generates different personalities for diff
     EXPECT(testParty[0].box.personality != testParty[1].box.personality);
     Free(testParty);
 }
+
+TEST("ModifyPersonalityForNature can set any nature")
+{
+    u32 personality, nature, j, k;
+    for (j = 0; j < 64; j++)
+    {
+        for (k = 0; k < NUM_NATURES; k++)
+        {
+            PARAMETRIZE { personality = Random32(); nature = k; }
+        }
+    }
+    ModifyPersonalityForNature(&personality, nature);
+    EXPECT_EQ(GetNatureFromPersonality(personality), nature);
+}