diff --git a/src/Bus.cpp b/src/Bus.cpp
index 1fe9c36..eb38615 100644
--- a/src/Bus.cpp
+++ b/src/Bus.cpp
@@ -93,6 +93,8 @@ Byte Bus::ReadCPU(Word addr)
 	{
 		return cartridge.ReadCPU(addr);
 	}
+
+	return 0x00;
 }
 
 Byte Bus::ReadPPU(Word addr)
diff --git a/src/mappers/Mapper000.cpp b/src/mappers/Mapper000.cpp
index 0e862c4..f3aa7ed 100644
--- a/src/mappers/Mapper000.cpp
+++ b/src/mappers/Mapper000.cpp
@@ -21,6 +21,8 @@ Byte Mapper000::ReadCPU(Word addr)
 	{
 		return PRG_ROM[addr & 0x03FFF];
 	}
+
+	return 0x00;
 }
 
 Byte Mapper000::ReadPPU(Word addr)
@@ -29,6 +31,8 @@ Byte Mapper000::ReadPPU(Word addr)
 	{
 		return CHR_ROM[addr];
 	}
+
+	return 0x00;
 }
 
 void Mapper000::WriteCPU(Word addr, Byte val)