diff --git a/BizHawk.Emulation.Cores/Consoles/Nintendo/NES/Boards/MMC3_family/Mapper187.cs b/BizHawk.Emulation.Cores/Consoles/Nintendo/NES/Boards/MMC3_family/Mapper187.cs
index dbc8858bf3..cb2da9c60e 100644
--- a/BizHawk.Emulation.Cores/Consoles/Nintendo/NES/Boards/MMC3_family/Mapper187.cs
+++ b/BizHawk.Emulation.Cores/Consoles/Nintendo/NES/Boards/MMC3_family/Mapper187.cs
@@ -1,115 +1,120 @@
-using BizHawk.Common;
-
-namespace BizHawk.Emulation.Cores.Nintendo.NES
-{
-	// Adapted from FCEUX src
-	public class Mapper187 : MMC3Board_Base
-	{
-		private ByteBuffer exRegs = new ByteBuffer(2);
-
-		private readonly byte[] prot_data = { 0x83, 0x83, 0x42, 0x00 };
-
-		public override bool Configure(NES.EDetectionOrigin origin)
-		{
-			switch (Cart.board_type)
-			{
-				case "MAPPER187":
-					break;
-				default:
-					return false;
-			}
-
-			BaseSetup();
-			return true;
-		}
-
-		public override void SyncState(Serializer ser)
-		{
-			base.SyncState(ser);
-			ser.Sync("expregs", ref exRegs);
-		}
-
-		public override void WritePRG(int addr, byte value)
-		{
-			if (addr == 0 || addr == 1)
-			{
-				exRegs[1] = value;
-			}
-
-			base.WritePRG(addr, value);
-		}
-
-		public override void WriteEXP(int addr, byte value)
-		{
-			if (addr == 0x1000) // 0x5000
-			{
-				exRegs[0] = value;
-			}
-
-			base.WriteEXP(addr, value);
-		}
-
-		public override void WriteWRAM(int addr, byte value)
-		{
-			if (addr == 0x6000)
-			{
-				exRegs[0] = value;
-			}
-
-			base.WriteWRAM(addr, value);
-		}
-
-		public override byte ReadEXP(int addr)
-		{
-			if (addr >= 0x1000)
-			{
-				return prot_data[exRegs[1] & 3];
-			}
-
-			return base.ReadEXP(addr);
-		}
-
-		private byte MMc3_cmd
-		{
-			get
-			{
-				return (byte)(mmc3.chr_mode ? 0x80 : 0);
-			}
-		}
-
-		protected override int Get_CHRBank_1K(int addr)
-		{
-			if ((addr & 0x1000) == ((MMc3_cmd & 0x80) << 5))
-			{
-				return base.Get_CHRBank_1K(addr) | 0x100;
-			}
-
-			return base.Get_CHRBank_1K(addr);
-		}
-
-		public override byte ReadPRG(int addr)
-		{
-			if ((exRegs[0] & 0x80) > 0)
-			{
-				var bank = exRegs[0] & 0x1F;
-				if ((exRegs[0] & 0x20) > 0)
-				{
-					if ((exRegs[0] & 0x40) > 0)
-					{
-						return ROM[((bank >> 2) << 15) + addr];
-					}
-					else
-					{
-						return ROM[((bank >> 1) << 15) + addr]; // hacky! two mappers in one! need real hw carts to test
-					}
-				}
-				else
-				{
-					return ROM[(bank << 14) + (addr & 0x3FFF)];
-				}
-			}
-
-			return base.ReadPRG(addr);
-		}
-	}
-}
+using BizHawk.Common;
+
+namespace BizHawk.Emulation.Cores.Nintendo.NES
+{
+	// Adapted from FCEUX src
+	public class Mapper187 : MMC3Board_Base
+	{
+		private ByteBuffer exRegs = new ByteBuffer(2);
+
+		private readonly byte[] prot_data = { 0x83, 0x83, 0x42, 0x00 };
+
+		public override bool Configure(NES.EDetectionOrigin origin)
+		{
+			switch (Cart.board_type)
+			{
+				case "MAPPER187":
+					break;
+				default:
+					return false;
+			}
+
+			BaseSetup();
+			return true;
+		}
+
+		public override void SyncState(Serializer ser)
+		{
+			base.SyncState(ser);
+			ser.Sync("expregs", ref exRegs);
+		}
+
+		public override void WritePRG(int addr, byte value)
+		{
+			if (addr == 0)
+			{
+				exRegs[1] = 1;
+				base.WritePRG(addr, value);
+			}
+			else if ((addr == 0x0001) && (exRegs[1] > 0))
+			{
+				base.WritePRG(addr, value);
+			}
+			else 
+				base.WritePRG(addr, value);
+		}
+
+		public override void WriteEXP(int addr, byte value)
+		{
+			if (addr == 0x1000) // 0x5000
+			{
+				exRegs[0] = value;
+			}
+
+			base.WriteEXP(addr, value);
+		}
+
+		public override void WriteWRAM(int addr, byte value)
+		{
+			if (addr == 0x0000)
+			{
+				exRegs[0] = value;
+			}
+
+			base.WriteWRAM(addr, value);
+		}
+
+		public override byte ReadEXP(int addr)
+		{
+			if (addr >= 0x1000)
+			{
+				return prot_data[exRegs[1] & 3];
+			}
+
+			return base.ReadEXP(addr);
+		}
+
+		private byte MMc3_cmd
+		{
+			get
+			{
+				return (byte)(mmc3.chr_mode ? 0x80 : 0);
+			}
+		}
+
+		protected override int Get_CHRBank_1K(int addr)
+		{
+			if ((addr & 0x1000) == ((MMc3_cmd & 0x80) << 5))
+			{
+				return base.Get_CHRBank_1K(addr) | 0x100;
+			}
+
+			return base.Get_CHRBank_1K(addr);
+		}
+
+		public override byte ReadPRG(int addr)
+		{
+			if ((exRegs[0] & 0x80) > 0)
+			{
+				var bank = exRegs[0] & 0x1F;
+				if ((exRegs[0] & 0x20) > 0)
+				{
+					if ((exRegs[0] & 0x40) > 0)
+					{
+						return ROM[((bank >> 2) << 15) + addr];
+					}
+					else
+					{
+						return ROM[((bank >> 1) << 15) + addr]; // hacky! two mappers in one! need real hw carts to test
+					}
+				}
+				else
+				{
+					return ROM[(bank << 14) + (addr & 0x3FFF)];
+				}
+			}
+
+			return base.ReadPRG(addr);
+		}
+	}
+}