diff --git a/src/hardware/vga_attr.cpp b/src/hardware/vga_attr.cpp
index 3d4c6b9d..953b4521 100644
--- a/src/hardware/vga_attr.cpp
+++ b/src/hardware/vga_attr.cpp
@@ -40,6 +40,7 @@ void write_p3c0(Bit32u port,Bit8u val) {
 		case 0x04:		case 0x05:		case 0x06:		case 0x07:
 		case 0x08:		case 0x09:		case 0x0a:		case 0x0b:
 		case 0x0c:		case 0x0d:		case 0x0e:		case 0x0f:
+			val&=0x3f;
 			attr(palette[attr(index)])=val;
 			VGA_DAC_CombineColor(attr(index),val);
 			/*