diff --git a/emulator/cpus/z80/src/execute.rs b/emulator/cpus/z80/src/execute.rs
index 3c93f80..462b368 100644
--- a/emulator/cpus/z80/src/execute.rs
+++ b/emulator/cpus/z80/src/execute.rs
@@ -106,7 +106,7 @@ impl Z80 {
 
                 let (result1, carry1, overflow1, half_carry1) = add_bytes(acc, self.get_flag(Flags::Carry) as u8);
                 let (result2, carry2, overflow2, half_carry2) = add_bytes(result1, src);
-                self.set_arithmetic_op_flags(result2 as u16, Size::Byte, false, carry1 | carry2, overflow1 | overflow2, half_carry1 | half_carry2);
+                self.set_arithmetic_op_flags(result2 as u16, Size::Byte, false, carry1 | carry2, overflow1 ^ overflow2, half_carry1 | half_carry2);
 
                 self.set_register_value(Register::A, result2);
             },
@@ -114,9 +114,9 @@ impl Z80 {
                 let src = self.get_register_pair_value(src_pair);
                 let dest = self.get_register_pair_value(dest_pair);
 
-                let (result1, carry1, overflow1, half_carry1) = add_words(dest, self.get_flag(Flags::Carry) as u16);
-                let (result2, carry2, overflow2, half_carry2) = add_words(result1, src);
-                self.set_arithmetic_op_flags(result2, Size::Word, false, carry1 | carry2, overflow1 | overflow2, half_carry1 | half_carry2);
+                let (result1, carry1, overflow1, half_carry1) = add_words(dest, src);
+                let (result2, carry2, overflow2, half_carry2) = add_words(result1, self.get_flag(Flags::Carry) as u16);
+                self.set_arithmetic_op_flags(result2, Size::Word, false, carry1 | carry2, overflow1 ^ overflow2, half_carry1 | half_carry2);
 
                 self.set_register_pair_value(dest_pair, result2);
             },
@@ -484,9 +484,9 @@ impl Z80 {
                 let src = self.get_target_value(target)?;
                 let acc = self.get_register_value(Register::A);
 
-                let (result1, carry1, overflow1) = sub_bytes(acc, self.get_flag(Flags::Carry) as u8);
-                let (result2, carry2, overflow2) = sub_bytes(result1, src);
-                self.set_arithmetic_op_flags(result2 as u16, Size::Byte, true, carry1 | carry2, overflow1 | overflow2, (result2 & 0x10) != 0);
+                let (result1, carry1, overflow1) = sub_bytes(acc, src);
+                let (result2, carry2, overflow2) = sub_bytes(result1, self.get_flag(Flags::Carry) as u8);
+                self.set_arithmetic_op_flags(result2 as u16, Size::Byte, true, carry1 | carry2, overflow1 ^ overflow2, (result2 & 0x10) != 0);
 
                 self.set_register_value(Register::A, result2);
             },
@@ -496,7 +496,7 @@ impl Z80 {
 
                 let (result1, carry1, overflow1) = sub_words(dest, self.get_flag(Flags::Carry) as u16);
                 let (result2, carry2, overflow2) = sub_words(result1, src);
-                self.set_arithmetic_op_flags(result2, Size::Word, true, carry1 | carry2, overflow1 | overflow2, (result2 & 0x10) != 0);
+                self.set_arithmetic_op_flags(result2, Size::Word, true, carry1 | carry2, overflow1 ^ overflow2, (result2 & 0x10) != 0);
 
                 self.set_register_pair_value(dest_pair, result2);
             },
@@ -858,27 +858,28 @@ impl Z80 {
 
 fn add_bytes(operand1: u8, operand2: u8) -> (u8, bool, bool, bool) {
     let (result, carry) = operand1.overflowing_add(operand2);
-    let (_, overflow) = (operand1 as i8).overflowing_add(operand2 as i8);
+    let overflow = (operand1 & 0x80) == (operand2 & 0x80) && (operand1 & 0x80) != (result & 0x80);
     let half_carry = (operand1 & 0x10) != 0 && (result & 0x10) == 0;
     (result, carry, overflow, half_carry)
 }
 
 fn add_words(operand1: u16, operand2: u16) -> (u16, bool, bool, bool) {
     let (result, carry) = operand1.overflowing_add(operand2);
-    let (_, overflow) = ((operand1 as i8) as i16).overflowing_add((operand2 as i8) as i16);
+    let overflow = (operand1 & 0x8000) == (operand2 & 0x8000) && (operand1 & 0x8000) != (result & 0x8000);
+    // TODO this is probably still wrong
     let half_carry = (operand1 & 0x10) != 0 && (result & 0x10) == 0;
     (result, carry, overflow, half_carry)
 }
 
 fn sub_bytes(operand1: u8, operand2: u8) -> (u8, bool, bool) {
     let (result, carry) = operand1.overflowing_sub(operand2);
-    let (_, overflow) = (operand1 as i8).overflowing_sub(operand2 as i8);
+    let overflow = (operand1 & 0x80) != (operand2 & 0x80) && (operand1 & 0x80) != (result & 0x80);
     (result, carry, overflow)
 }
 
 fn sub_words(operand1: u16, operand2: u16) -> (u16, bool, bool) {
     let (result, carry) = operand1.overflowing_sub(operand2);
-    let (_, overflow) = ((operand1 as i8) as i16).overflowing_sub((operand2 as i8) as i16);
+    let overflow = (operand1 & 0x8000) != (operand2 & 0x8000) && (operand1 & 0x8000) != (result & 0x8000);
     (result, carry, overflow)
 }
 
diff --git a/tests/rad_tests/latest.txt b/tests/rad_tests/latest.txt
index 2257a33..cf56936 100644
--- a/tests/rad_tests/latest.txt
+++ b/tests/rad_tests/latest.txt
@@ -1,4 +1,4 @@
-Last run on 2023-05-12 at commit b2b9d73375d0ae7822cd3b1376b706f94b0b4456
+Last run on 2023-05-13 at commit d8638c6f82f45f6235784f96d8f5eb1a766bad52
 
 00.json completed, all passed!
 01.json completed, all passed!
@@ -138,12 +138,12 @@ Last run on 2023-05-12 at commit b2b9d73375d0ae7822cd3b1376b706f94b0b4456
 85.json completed, all passed!
 86.json completed, all passed!
 87.json completed, all passed!
-88.json completed: 999 passed, 1 FAILED
+88.json completed, all passed!
 89.json completed, all passed!
 8a.json completed, all passed!
 8b.json completed, all passed!
 8c.json completed, all passed!
-8d.json completed: 999 passed, 1 FAILED
+8d.json completed, all passed!
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 8f.json completed, all passed!
 90.json completed, all passed!
@@ -154,14 +154,14 @@ Last run on 2023-05-12 at commit b2b9d73375d0ae7822cd3b1376b706f94b0b4456
 95.json completed, all passed!
 96.json completed, all passed!
 97.json completed, all passed!
-98.json completed: 998 passed, 2 FAILED
-99.json completed: 999 passed, 1 FAILED
-9a.json completed: 998 passed, 2 FAILED
-9b.json completed: 999 passed, 1 FAILED
-9c.json completed: 999 passed, 1 FAILED
-9d.json completed: 999 passed, 1 FAILED
-9e.json completed: 998 passed, 2 FAILED
-9f.json completed: 996 passed, 4 FAILED
+98.json completed, all passed!
+99.json completed, all passed!
+9a.json completed, all passed!
+9b.json completed, all passed!
+9c.json completed, all passed!
+9d.json completed, all passed!
+9e.json completed, all passed!
+9f.json completed, all passed!
 a0.json completed, all passed!
 a1.json completed, all passed!
 a2.json completed, all passed!
@@ -455,7 +455,7 @@ cb fe.json completed, all passed!
 cb ff.json completed, all passed!
 cc.json completed, all passed!
 cd.json completed, all passed!
-ce.json completed: 998 passed, 2 FAILED
+ce.json completed, all passed!
 cf.json completed, all passed!
 d0.json completed, all passed!
 d1.json completed, all passed!
@@ -489,7 +489,7 @@ dd 74.json completed, all passed!
 dd 75.json completed, all passed!
 dd 77.json completed, all passed!
 dd 7e.json completed, all passed!
-dd 8e.json completed: 998 passed, 2 FAILED
+dd 8e.json completed, all passed!
 dd 9e.json completed, all passed!
 dd ae.json completed, all passed!
 dd b6.json completed, all passed!
@@ -506,7 +506,7 @@ dd e9.json completed, all passed!
 dd ee.json completed: 0 passed, 1000 FAILED
 dd f9.json completed, all passed!
 dd fe.json completed: 0 passed, 1000 FAILED
-de.json completed: 998 passed, 2 FAILED
+de.json completed, all passed!
 df.json completed, all passed!
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 e1.json completed, all passed!
@@ -523,7 +523,7 @@ eb.json completed, all passed!
 ec.json completed, all passed!
 ed 40.json completed: 0 passed, 1000 FAILED
 ed 41.json completed: 0 passed, 1000 FAILED
-ed 42.json completed: 765 passed, 235 FAILED
+ed 42.json completed, all passed!
 ed 43.json completed, all passed!
 ed 44.json completed, all passed!
 ed 45.json completed: 0 passed, 1000 FAILED
@@ -531,7 +531,7 @@ ed 46.json completed, all passed!
 ed 47.json completed, all passed!
 ed 48.json completed: 0 passed, 1000 FAILED
 ed 49.json completed: 0 passed, 1000 FAILED
-ed 4a.json completed: 723 passed, 277 FAILED
+ed 4a.json completed, all passed!
 ed 4b.json completed, all passed!
 ed 4c.json completed, all passed!
 ed 4d.json completed: 0 passed, 1000 FAILED
@@ -539,7 +539,7 @@ ed 4e.json completed, all passed!
 ed 4f.json completed, all passed!
 ed 50.json completed: 0 passed, 1000 FAILED
 ed 51.json completed: 0 passed, 1000 FAILED
-ed 52.json completed: 746 passed, 254 FAILED
+ed 52.json completed, all passed!
 ed 53.json completed, all passed!
 ed 54.json completed, all passed!
 ed 55.json completed: 0 passed, 1000 FAILED
@@ -547,7 +547,7 @@ ed 56.json completed, all passed!
 ed 57.json completed: 0 passed, 1000 FAILED
 ed 58.json completed: 0 passed, 1000 FAILED
 ed 59.json completed: 0 passed, 1000 FAILED
-ed 5a.json completed: 743 passed, 257 FAILED
+ed 5a.json completed, all passed!
 ed 5b.json completed, all passed!
 ed 5c.json completed, all passed!
 ed 5d.json completed: 0 passed, 1000 FAILED
@@ -563,7 +563,7 @@ ed 66.json completed, all passed!
 ed 67.json completed: 0 passed, 1000 FAILED
 ed 68.json completed: 0 passed, 1000 FAILED
 ed 69.json completed: 0 passed, 1000 FAILED
-ed 6a.json completed: 486 passed, 514 FAILED
+ed 6a.json completed, all passed!
 ed 6b.json completed, all passed!
 ed 6c.json completed, all passed!
 ed 6d.json completed: 0 passed, 1000 FAILED
@@ -571,7 +571,7 @@ ed 6e.json completed, all passed!
 ed 6f.json completed: 0 passed, 1000 FAILED
 ed 70.json completed: 0 passed, 1000 FAILED
 ed 71.json completed: 0 passed, 1000 FAILED
-ed 72.json completed: 744 passed, 256 FAILED
+ed 72.json completed, all passed!
 ed 73.json completed, all passed!
 ed 74.json completed, all passed!
 ed 75.json completed: 0 passed, 1000 FAILED
@@ -579,7 +579,7 @@ ed 76.json completed, all passed!
 ed 77.json completed, all passed!
 ed 78.json completed: 0 passed, 1000 FAILED
 ed 79.json completed: 0 passed, 1000 FAILED
-ed 7a.json completed: 760 passed, 240 FAILED
+ed 7a.json completed, all passed!
 ed 7b.json completed, all passed!
 ed 7c.json completed, all passed!
 ed 7d.json completed: 0 passed, 1000 FAILED
@@ -635,8 +635,8 @@ fd 74.json completed, all passed!
 fd 75.json completed, all passed!
 fd 77.json completed, all passed!
 fd 7e.json completed, all passed!
-fd 8e.json completed: 999 passed, 1 FAILED
-fd 9e.json completed: 999 passed, 1 FAILED
+fd 8e.json completed, all passed!
+fd 9e.json completed, all passed!
 fd ae.json completed, all passed!
 fd b6.json completed, all passed!
 fd be.json completed, all passed!
@@ -655,5 +655,5 @@ fd fe.json completed: 0 passed, 1000 FAILED
 fe.json completed, all passed!
 ff.json completed, all passed!
 
-passed: 543908, failed: 110092, total 83%
-completed in 12m 50s
+passed: 545965, failed: 108035, total 83%
+completed in 10m 35s