diff --git a/PKHeX.Core/Util/ArrayUtil.cs b/PKHeX.Core/Util/ArrayUtil.cs
index 80af5dc0e..0773c3ad4 100644
--- a/PKHeX.Core/Util/ArrayUtil.cs
+++ b/PKHeX.Core/Util/ArrayUtil.cs
@@ -64,8 +64,12 @@ public static void SetBitFlagArray(byte[] data, int offset, bool[] value)
         {
             for (int i = 0; i < value.Length; i++)
             {
+                var ofs = offset + (i >> 3);
+                var mask = (1 << (i & 7));
                 if (value[i])
-                    data[offset + (i >> 3)] |= (byte)(1 << (i & 7));
+                    data[ofs] |= (byte)mask;
+                else
+                    data[ofs] &= (byte)~mask;
             }
         }