diff --git a/include/config.h b/include/config.h
index 2ad84f29cd..9412c8f426 100644
--- a/include/config.h
+++ b/include/config.h
@@ -6,7 +6,7 @@
 // still has them in the ROM. This is because the developers forgot
 // to define NDEBUG before release, however this has been changed as
 // Ruby's actual debug build does not use the AGBPrint features.
-#define NDEBUG
+// #define NDEBUG
 
 // To enable printf debugging, comment out "#define NDEBUG". This allows
 // the various AGBPrint functions to be used. (See include/gba/isagbprint.h).
diff --git a/include/test_runner.h b/include/test_runner.h
index 27b0d59777..91f6f8f436 100644
--- a/include/test_runner.h
+++ b/include/test_runner.h
@@ -17,6 +17,8 @@ void TestRunner_Battle_AfterLastTurn(void);
 
 void TestRunner_Battle_CheckBattleRecordActionType(u32 battlerId, u32 recordIndex, u32 actionType);
 
+u32 TestRunner_Battle_GetForcedAbility(u32 side, u32 partyIndex);
+
 #else
 
 #define TestRunner_Battle_RecordAbilityPopUp(...) (void)0
@@ -28,6 +30,8 @@ void TestRunner_Battle_CheckBattleRecordActionType(u32 battlerId, u32 recordInde
 
 #define TestRunner_Battle_CheckBattleRecordActionType(...) (void)0
 
+#define TestRunner_Battle_GetForcedAbility(...) (u32)0
+
 #endif
 
 #endif
diff --git a/src/battle_main.c b/src/battle_main.c
index 270447a0e1..9795834530 100644
--- a/src/battle_main.c
+++ b/src/battle_main.c
@@ -3302,6 +3302,14 @@ void SwitchInClearSetData(void)
     // Clear selected party ID so Revival Blessing doesn't get confused.
     gSelectedMonPartyId = PARTY_SIZE;
 
+    // Allow for illegal abilities within tests.
+    if (gTestRunnerEnabled)
+    {
+        u32 side = GetBattlerSide(gActiveBattler);
+        u32 partyIndex = gBattlerPartyIndexes[gActiveBattler];
+        gBattleMons[gActiveBattler].ability = gBattleStruct->overwrittenAbilities[gActiveBattler] = TestRunner_Battle_GetForcedAbility(side, partyIndex);
+    }
+
     Ai_UpdateSwitchInData(gActiveBattler);
 }
 
@@ -3794,6 +3802,18 @@ static void TryDoEventsBeforeFirstTurn(void)
         }
     }
 
+    // Allow for illegal abilities within tests.
+    if (gTestRunnerEnabled && gBattleStruct->switchInAbilitiesCounter == 0)
+    {
+        for (i = 0; i < gBattlersCount; ++i)
+        {
+            u32 side = GetBattlerSide(i);
+            u32 partyIndex = gBattlerPartyIndexes[i];
+            if (TestRunner_Battle_GetForcedAbility(side, partyIndex))
+                gBattleMons[i].ability = gBattleStruct->overwrittenAbilities[i] = TestRunner_Battle_GetForcedAbility(side, partyIndex);
+        }
+    }
+
     if (gBattleStruct->switchInAbilitiesCounter == 0)
     {
         for (i = 0; i < gBattlersCount; i++)
diff --git a/test/test_battle.h b/test/test_battle.h
index 205c699192..bd8061f422 100644
--- a/test/test_battle.h
+++ b/test/test_battle.h
@@ -574,6 +574,7 @@ struct BattleTestData
     struct Pokemon *currentMon;
     u8 gender;
     u8 nature;
+    u16 forcedAbilities[NUM_BATTLE_SIDES][PARTY_SIZE];
 
     u8 currentMonIndexes[MAX_BATTLERS_COUNT];
     u8 turnState;
diff --git a/test/test_runner_battle.c b/test/test_runner_battle.c
index d1feaee02a..8358536248 100644
--- a/test/test_runner_battle.c
+++ b/test/test_runner_battle.c
@@ -1090,7 +1090,14 @@ void Ability_(u32 sourceLine, u32 ability)
             break;
         }
     }
-    INVALID_IF(i == NUM_ABILITY_SLOTS, "%S cannot have %S", gSpeciesNames[species], gAbilityNames[ability]);
+
+    // Store forced ability to be set when the battle starts if invalid.
+    if (i == NUM_ABILITY_SLOTS)
+    {
+        DATA.forcedAbilities[DATA.currentSide][DATA.currentPartyIndex] = ability;
+    }
+        
+    // INVALID_IF(i == NUM_ABILITY_SLOTS, "%S cannot have %S", gSpeciesNames[species], gAbilityNames[ability]);
 }
 
 void Level_(u32 sourceLine, u32 level)
@@ -1774,3 +1781,8 @@ void ValidateFinally(u32 sourceLine)
         return;
     INVALID_IF(STATE->parametersCount == 0, "FINALLY without PARAMETRIZE");
 }
+
+u32 TestRunner_Battle_GetForcedAbility(u32 side, u32 partyIndex)
+{
+    return DATA.forcedAbilities[side][partyIndex];
+}