diff --git a/PKHeX.Core/Legality/Restrictions/Vivillon3DS.cs b/PKHeX.Core/Legality/Restrictions/Vivillon3DS.cs
index b3ddc2fc6..8f155e7f9 100644
--- a/PKHeX.Core/Legality/Restrictions/Vivillon3DS.cs
+++ b/PKHeX.Core/Legality/Restrictions/Vivillon3DS.cs
@@ -204,11 +204,15 @@ internal FormSubregionTable(byte form, byte[] regions)
                 new FormSubregionTable(17, new byte[] {12})),
         };
 
+        public const int MaxWildFormID = 17; // 0-17 valid form indexes
+
         /// <summary>
         /// Compares the Vivillon pattern against its console region to determine if the pattern is legal.
         /// </summary>
         public static bool IsPatternValid(int form, int consoleRegion)
         {
+            if ((uint)form > MaxWildFormID)
+                return false;
             var permit = GetConsoleRegionFlag(consoleRegion);
             return VivillonRegionTable[form].HasFlag(permit);
         }
@@ -222,11 +226,13 @@ public static bool IsPatternValid(int form, int consoleRegion)
         /// <returns>True if valid</returns>
         public static bool IsPatternNative(int form, byte country, byte region)
         {
+            if ((uint)form > MaxWildFormID)
+                return false;
             if (!VivillonCountryTable[form].Contains(country))
                 return false; // Country mismatch
 
             var ct = Array.Find(RegionFormTable, t => t.CountryID == country);
-            if (ct == default(CountryTable)) // empty = one form for country
+            if (ct == null) // empty = one form for country
                 return true; // No subregion table, already checked if Country can have this form
 
             if (ct.BaseForm == form)
@@ -243,7 +249,7 @@ public static bool IsPatternNative(int form, byte country, byte region)
         public static int GetPattern(byte country, byte region)
         {
             var ct = Array.Find(RegionFormTable, t => t.CountryID == country);
-            if (ct == default(CountryTable)) // empty = no forms referenced
+            if (ct == null) // empty = no forms referenced
                 return GetPattern(country);
 
             foreach (var sub in ct.SubRegionForms)
diff --git a/PKHeX.Core/Legality/Tables/FormInfo.cs b/PKHeX.Core/Legality/Tables/FormInfo.cs
index b34120f27..6777c9e14 100644
--- a/PKHeX.Core/Legality/Tables/FormInfo.cs
+++ b/PKHeX.Core/Legality/Tables/FormInfo.cs
@@ -251,8 +251,8 @@ public static int GetTotemBaseForm(int species, int form)
             Unown => form < (format == 2 ? 26 : 28), // A-Z : A-Z?!
             Mothim => form < 3, // Burmy base form is kept
 
-            Scatterbug => form < 18, // Vivillon Pre-evolutions
-            Spewpa => form < 18, // Vivillon Pre-evolutions
+            Scatterbug => form <= Vivillon3DS.MaxWildFormID, // Vivillon Pre-evolutions
+            Spewpa => form <= Vivillon3DS.MaxWildFormID, // Vivillon Pre-evolutions
 
             _ => false
         };
diff --git a/PKHeX.Core/Legality/Verifiers/FormVerifier.cs b/PKHeX.Core/Legality/Verifiers/FormVerifier.cs
index 9980e789b..5a3c6e4af 100644
--- a/PKHeX.Core/Legality/Verifiers/FormVerifier.cs
+++ b/PKHeX.Core/Legality/Verifiers/FormVerifier.cs
@@ -98,7 +98,7 @@ private CheckResult VerifyForm(LegalityAnalysis data)
                     break;
 
                 case Scatterbug or Spewpa:
-                    if (form > 17) // Fancy & Pokéball
+                    if (form > Vivillon3DS.MaxWildFormID) // Fancy & Pokéball
                         return GetInvalid(LFormVivillonEventPre);
                     if (pkm is not IRegionOrigin tr)
                         break;
@@ -108,7 +108,7 @@ private CheckResult VerifyForm(LegalityAnalysis data)
                         data.AddLine(Get(LFormVivillonNonNative, Severity.Fishy));
                     break;
                 case Vivillon:
-                    if (form > 17) // Fancy & Pokéball
+                    if (form > Vivillon3DS.MaxWildFormID) // Fancy & Pokéball
                     {
                         if (enc is not MysteryGift)
                             return GetInvalid(LFormVivillonInvalid);