diff --git a/BizHawk.Emulation.Cores/BizHawk.Emulation.Cores.csproj b/BizHawk.Emulation.Cores/BizHawk.Emulation.Cores.csproj
index bab896a280..40161b6902 100644
--- a/BizHawk.Emulation.Cores/BizHawk.Emulation.Cores.csproj
+++ b/BizHawk.Emulation.Cores/BizHawk.Emulation.Cores.csproj
@@ -616,6 +616,7 @@
     <Compile Include="Consoles\Nintendo\NES\Boards\Mapper108.cs" />
     <Compile Include="Consoles\Nintendo\NES\Boards\Mapper116.cs" />
     <Compile Include="Consoles\Nintendo\NES\Boards\Mapper120.cs" />
+    <Compile Include="Consoles\Nintendo\NES\Boards\Mapper125.cs" />
     <Compile Include="Consoles\Nintendo\NES\Boards\Mapper132.cs" />
     <Compile Include="Consoles\Nintendo\NES\Boards\Mapper136.cs" />
     <Compile Include="Consoles\Nintendo\NES\Boards\Mapper142.cs" />
diff --git a/BizHawk.Emulation.Cores/Consoles/Nintendo/NES/Boards/Mapper125.cs b/BizHawk.Emulation.Cores/Consoles/Nintendo/NES/Boards/Mapper125.cs
new file mode 100644
index 0000000000..32838416dd
--- /dev/null
+++ b/BizHawk.Emulation.Cores/Consoles/Nintendo/NES/Boards/Mapper125.cs
@@ -0,0 +1,58 @@
+using BizHawk.Common;
+
+
+namespace BizHawk.Emulation.Cores.Nintendo.NES
+{
+	public sealed class Mapper125 : NES.NESBoardBase
+	{
+		private byte reg;
+		private int prg_bank_mask_8k;
+
+		public override bool Configure(NES.EDetectionOrigin origin)
+		{
+
+			switch (Cart.board_type)
+			{
+				case "MAPPER125":
+				case "UNIF_UNL-LH32":
+					break;
+				default:
+					return false;
+			}
+
+			prg_bank_mask_8k = Cart.prg_size / 8 - 1;
+			return true;
+		}
+
+		public override void SyncState(Serializer ser)
+		{
+			ser.Sync("reg", ref reg);
+			base.SyncState(ser);
+		}
+
+		public override void WriteWRAM(int addr, byte value)
+		{
+			if (addr == 0)
+			{
+				reg = value;
+			}
+		}
+
+		public override byte ReadPRG(int addr)
+		{
+			int bank = 0;
+			if (addr < 0x2000) { bank = prg_bank_mask_8k - 3; }
+			else if (addr < 0x4000) { bank = prg_bank_mask_8k - 2; }
+			else if (addr < 0x6000) { bank = prg_bank_mask_8k - 1; }
+			else { bank = prg_bank_mask_8k; }
+
+			bank &= prg_bank_mask_8k;
+			return ROM[(bank << 13) + (addr & 0x1FFF)];
+		}
+
+		public override byte ReadWRAM(int addr)
+		{
+			return ROM[((reg & prg_bank_mask_8k) << 13) + addr];
+		}
+	}
+}