diff --git a/src/emulator/main.rs b/src/emulator/main.rs
index 510ee7d..7c9fffb 100644
--- a/src/emulator/main.rs
+++ b/src/emulator/main.rs
@@ -116,20 +116,20 @@ fn tick(state: &mut EmulatorState) {
         0x37 => state.cc.c = true,        // STC
         0x3f => state.cc.c = !state.cc.c, // CMC
 
-        0x80..=0x87 => arithmetic::add_reg(register_from_num(instruction & 0xf), false, state), // ADD
-        0x88..=0x8f => arithmetic::add_reg(register_from_num(instruction & 0xf), state.cc.c, state), // ADC
+        0x80..=0x87 => arithmetic::add_reg(register_from_num(instruction & 0x7), false, state), // ADD
+        0x88..=0x8f => arithmetic::add_reg(register_from_num(instruction & 0x7), state.cc.c, state), // ADC
         0xc6 => arithmetic::add(next_byte(), false, state), // ADI
         0xce => arithmetic::add(next_byte(), state.cc.c, state), // ACI
 
-        0x90..=0x97 => arithmetic::sub_reg(register_from_num(instruction & 0xf), false, state), // SUB
-        0x98..=0x9f => arithmetic::sub_reg(register_from_num(instruction & 0xf), state.cc.c, state), // SBB
+        0x90..=0x97 => arithmetic::sub_reg(register_from_num(instruction & 0x7), false, state), // SUB
+        0x98..=0x9f => arithmetic::sub_reg(register_from_num(instruction & 0x7), state.cc.c, state), // SBB
         0xd6 => arithmetic::sub(next_byte(), false, state), // SUI
         0xde => arithmetic::sub(next_byte(), state.cc.c, state), // SBI
 
-        0xa0..=0xa7 => arithmetic::and_reg(register_from_num(instruction & 0xf), state), // ANA
-        0xa8..=0xaf => arithmetic::xor_reg(register_from_num(instruction & 0xf), state), // XRA
-        0xb0..=0xb7 => arithmetic::or_reg(register_from_num(instruction & 0xf), state),  // ORA
-        0xb8..=0xbf => arithmetic::cmp_reg(register_from_num(instruction & 0xf), state), // CMP
+        0xa0..=0xa7 => arithmetic::and_reg(register_from_num(instruction & 0x7), state), // ANA
+        0xa8..=0xaf => arithmetic::xor_reg(register_from_num(instruction & 0x7), state), // XRA
+        0xb0..=0xb7 => arithmetic::or_reg(register_from_num(instruction & 0x7), state),  // ORA
+        0xb8..=0xbf => arithmetic::cmp_reg(register_from_num(instruction & 0x7), state), // CMP
         0xe6 => arithmetic::and(next_byte(), state),                                     // ANI
         0xee => arithmetic::xor(next_byte(), state),                                     // XRI
         0xf6 => arithmetic::or(next_byte(), state),                                      // ORI
diff --git a/src/emulator/structs.rs b/src/emulator/structs.rs
index 2a4171f..7248023 100644
--- a/src/emulator/structs.rs
+++ b/src/emulator/structs.rs
@@ -51,6 +51,7 @@ pub enum Register {
 }
 
 /// Returns a Register enum based on the input number 0..7 in the order B,C,D,E,H,L,M,A
+#[track_caller]
 pub fn register_from_num(b: u8) -> Register {
     match b {
         0 => Register::B,