diff --git a/src/chip8.cpp b/src/chip8.cpp
index c6e1107..2cb1bad 100644
--- a/src/chip8.cpp
+++ b/src/chip8.cpp
@@ -282,12 +282,12 @@ void Chip8::Exec(const opcode_t& opc) {
     X("OR Vx Vy"   , prefix == 0x8 && n == 0x1     , Vx |= Vy;) \
     X("AND Vx Vy"  , prefix == 0x8 && n == 0x2     , Vx &= Vy;) \
     X("XOR Vx Vy"  , prefix == 0x8 && n == 0x3     , Vx ^= Vy;) \
-    X("ADD Vx Vy"  , prefix == 0x8 && n == 0x4     , Vf = ((Vx & 0x80) >> 7) & ((Vy & 0x80) >> 7); Vx += Vy;) \
-    X("SUB Vx Vy"  , prefix == 0x8 && n == 0x5     , Vf = (Vx > Vy) ? 1 : 0; Vx -= Vy;) \
-    X("SHR Vx Vy"  , prefix == 0x8 && n == 0x6     , Vf = Vx & 1; Vx >>= 1;) \
-    X("SUBN Vx Vy" , prefix == 0x8 && n == 0x7     , Vf = (Vy > Vx) ? 1 : 0; Vx = Vy - Vx;) \
-    X("SHL Vx Vy"  , prefix == 0x8 && n == 0xe     , Vf = (Vx >> 7) & 0x1; Vx <<= 1;) \
-    X("SNE Vx Vy"  , prefix == 0x9 && n == 0 \
+    X("ADD Vx Vy"  , prefix == 0x8 && n == 0x4     , uint16_t sum = Vx + Vy; Vf = sum > 0x100; Vx = sum & 0xFF;) \
+    X("SUB Vx Vy"  , prefix == 0x8 && n == 0x5     , Vf = Vx >= Vy; Vx = (Vx - Vy) & 0xFF) \
+    X("SHR Vx Vy"  , prefix == 0x8 && n == 0x6     , Vf = Vx & 0x1; Vx >>= 1;) \
+    X("SUBN Vx Vy" , prefix == 0x8 && n == 0x7     , Vf = Vy >= Vx; Vx = (Vy - Vx) & 0xFF;) \
+    X("SHL Vx Vy"  , prefix == 0x8 && n == 0xe     , Vf = (Vx >> 7) & 0x1; Vx = (Vx << 1) & 0xFF;) \
+    X("SNE Vx Vy"  , prefix == 0x9 && n == 0x0 \
                                    && Vx != Vy     , PC += 2;) \
     X("LD I nnn"   , prefix == 0xa                 , I = nnn;) \
     X("JP V0 nnn"  , prefix == 0xb                 , PC = nnn + regs_[0] - 2;) \