diff --git a/PKHeX.Core/Editing/Pokerus.cs b/PKHeX.Core/Editing/Pokerus.cs
index fea80b73a..7aff49a57 100644
--- a/PKHeX.Core/Editing/Pokerus.cs
+++ b/PKHeX.Core/Editing/Pokerus.cs
@@ -49,16 +49,23 @@ public static bool IsStrainValid(PKM pk, int strain, int days)
     {
         if (!IsObtainable(pk))
             return IsSusceptible(strain, days);
-        return IsStrainValid(strain, days);
+        if (pk.Format <= 2)
+            return IsStrainValid2(strain);
+        return IsStrainValid(strain);
     }
 
     /// <inheritdoc cref="IsStrainValid(PKM,int,int)"/>
-    public static bool IsStrainValid(int strain, int days) => strain switch
-    {
-        0 when days is not 0 => false,
-        8 => false,
-        _ => true,
-    };
+    /// <remarks>
+    /// Strains 9+ are not obtainable due to game programming error (jmp label too early).
+    /// </remarks>
+    public static bool IsStrainValid2(int strain) => strain <= 8;
+
+    /// <inheritdoc cref="IsStrainValid(PKM,int,int)"/>
+    /// <remarks>
+    /// Gen3 R/S have a 30/255 chance of giving strain 0, and a 1/255 chance of giving strain 8.
+    /// Transfers will retain strain 0/8 and they're still able to infect others.
+    /// </remarks>
+    public static bool IsStrainValid(int strain) => strain <= 0xF;
 
     /// <summary>
     /// Checks if the Pokérus value for Duration is possible to have on the input entity.
@@ -88,7 +95,7 @@ public static bool IsDurationValid(int strain, int days, out int max)
     /// <param name="strain">Strain number</param>
     /// <param name="days">Duration remaining</param>
     /// <returns>True if currently infected, and infectious to others.</returns>
-    public static bool IsInfectuous(int strain, int days) => strain != 0 && days != 0;
+    public static bool IsInfectious(int strain, int days) => days != 0;
 
     /// <summary>
     /// Checks if the Pokémon can be infected with the Pokérus.
diff --git a/PKHeX.Core/PKM/PKM.cs b/PKHeX.Core/PKM/PKM.cs
index 376e8bf16..fed0967b5 100644
--- a/PKHeX.Core/PKM/PKM.cs
+++ b/PKHeX.Core/PKM/PKM.cs
@@ -318,7 +318,7 @@ public int Generation
         }
     }
 
-    public bool PKRS_Infected { get => PKRS_Strain != 0; set => PKRS_Strain = value ? Math.Max(PKRS_Strain, 1) : 0; }
+    public bool PKRS_Infected { get => PKRS_Days != 0; set => PKRS_Strain = value ? Math.Max(PKRS_Strain, 1) : 0; }
 
     public bool PKRS_Cured
     {
diff --git a/PKHeX.WinForms/Controls/PKM Editor/LoadSave.cs b/PKHeX.WinForms/Controls/PKM Editor/LoadSave.cs
index aed3e31cb..9948abf78 100644
--- a/PKHeX.WinForms/Controls/PKM Editor/LoadSave.cs	
+++ b/PKHeX.WinForms/Controls/PKM Editor/LoadSave.cs	
@@ -56,9 +56,10 @@ private void SaveOT(PKM pk)
 
     private void LoadPKRS(PKM pk)
     {
-        Label_PKRS.Visible = CB_PKRSStrain.Visible = CHK_Infected.Checked = Label_PKRSdays.Visible = CB_PKRSDays.Visible = pk.PKRS_Infected;
-        LoadClamp(CB_PKRSStrain, pk.PKRS_Strain);
+        CHK_Infected.Checked = Label_PKRS.Visible = Label_PKRSdays.Visible = CB_PKRSStrain.Visible = CB_PKRSDays.Visible = pk.PKRS_Infected;
         CHK_Cured.Checked = pk.PKRS_Cured;
+        ChangePKRSstrainDropDownLists(CB_PKRSStrain.SelectedIndex, pk.PKRS_Strain, 0);
+        LoadClamp(CB_PKRSStrain, pk.PKRS_Strain);
         LoadClamp(CB_PKRSDays, pk.PKRS_Days); // clamp to valid day values for the current strain
     }
 
diff --git a/PKHeX.WinForms/Controls/PKM Editor/PKMEditor.cs b/PKHeX.WinForms/Controls/PKM Editor/PKMEditor.cs
index 49048c7d9..8beb62e66 100644
--- a/PKHeX.WinForms/Controls/PKM Editor/PKMEditor.cs	
+++ b/PKHeX.WinForms/Controls/PKM Editor/PKMEditor.cs	
@@ -1043,21 +1043,32 @@ private void RefreshFormArguments()
 
     private void UpdatePKRSstrain(object sender, EventArgs e)
     {
-        // Change the PKRS Days to the legal bounds.
-        int currentDuration = CB_PKRSDays.SelectedIndex;
-        CB_PKRSDays.Items.Clear();
+        if (!FieldsLoaded)
+            return;
 
-        var strain = CB_PKRSStrain.SelectedIndex;
-        int max = Pokerus.GetMaxDuration(strain);
+        // Change the PKRS Days to the legal bounds.
+        ChangePKRSstrainDropDownLists(-1, CB_PKRSStrain.SelectedIndex, CB_PKRSDays.SelectedIndex);
+    }
+
+    private void ChangePKRSstrainDropDownLists(int oldStrain, int newStrain, int currentDuration)
+    {
+        if (oldStrain == newStrain)
+            return;
+
+        CB_PKRSDays.Items.Clear();
+        int max = Pokerus.GetMaxDuration(newStrain);
         for (int day = 0; day <= max; day++)
             CB_PKRSDays.Items.Add(day.ToString());
 
         // Set the days back if they're legal
-        CB_PKRSDays.SelectedIndex = strain == 0 ? 0 : Math.Min(max, currentDuration);
+        CB_PKRSDays.SelectedIndex = Math.Min(max, currentDuration);
     }
 
     private void UpdatePKRSdays(object sender, EventArgs e)
     {
+        if (!FieldsLoaded)
+            return;
+
         var days = CB_PKRSDays.SelectedIndex;
         if (days != 0)
             return;
@@ -1072,19 +1083,22 @@ private void UpdatePKRSdays(object sender, EventArgs e)
 
     private void UpdatePKRSCured(object sender, EventArgs e)
     {
+        if (!FieldsLoaded)
+            return;
+
         // Cured PokeRus is toggled
         if (CHK_Cured.Checked)
         {
+            // If we're cured we have to have a strain infection.
+            if (CB_PKRSStrain.SelectedIndex == 0)
+                CB_PKRSStrain.SelectedIndex = 1;
+
             // Has Had PokeRus
             Label_PKRSdays.Visible = CB_PKRSDays.Visible = false;
             CB_PKRSDays.SelectedIndex = 0;
 
             Label_PKRS.Visible = CB_PKRSStrain.Visible = true;
             CHK_Infected.Checked = true;
-
-            // If we're cured we have to have a strain infection.
-            if (CB_PKRSStrain.SelectedIndex == 0)
-                CB_PKRSStrain.SelectedIndex = 1;
         }
         else if (!CHK_Infected.Checked)
         {
@@ -1107,6 +1121,9 @@ private void UpdatePKRSCured(object sender, EventArgs e)
 
     private void UpdatePKRSInfected(object sender, EventArgs e)
     {
+        if (!FieldsLoaded)
+            return;
+
         if (CHK_Cured.Checked)
         {
             if (!CHK_Infected.Checked)