diff --git a/src/cpus/m68k/decode.rs b/src/cpus/m68k/decode.rs
index 13b9286..27f46d5 100644
--- a/src/cpus/m68k/decode.rs
+++ b/src/cpus/m68k/decode.rs
@@ -179,11 +179,9 @@ impl M68kDecoder {
                     if (ins & 0x040) == 0 {
                         let size = match get_size(ins) {
                             Some(Size::Word) => Size::Word,
-                            // TODO 2021-12-14: the docs for the 68000 show the size field, even though it says it only operates on words
-                            //                  and according to some other sources, it seems they are parsed and executed on the 68000, so
-                            //                  I'm removing the check that only allows this on the MC68020
-                            //Some(Size::Long) if self.cputype >= M68kType::MC68020 => Size::Long,
-                            Some(Size::Long) => Size::Long,
+                            Some(Size::Long) if self.cputype >= M68kType::MC68020 => Size::Long,
+                            // On the 68000, long words in CHK are not supported, but the opcode maps to the word size instruction
+                            Some(Size::Long) => Size::Word,
                             _ => return Err(Error::processor(Exceptions::IllegalInstruction as u32)),
                         };
 
diff --git a/src/cpus/m68k/execute.rs b/src/cpus/m68k/execute.rs
index 00406d9..7f1fe87 100644
--- a/src/cpus/m68k/execute.rs
+++ b/src/cpus/m68k/execute.rs
@@ -381,8 +381,20 @@ impl M68k {
             },
             //Instruction::BKPT(u8) => {
             //},
-            //Instruction::CHK(Target, Size) => {
-            //},
+            Instruction::CHK(target, reg, size) => {
+                let upper_bound = sign_extend_to_long(self.get_target_value(target, size, Used::Once)?, size) as i32;
+                let dreg = sign_extend_to_long(self.state.d_reg[reg as usize], size) as i32;
+
+                self.set_sr(self.state.sr & 0xFFF0);
+                if dreg < 0 || dreg > upper_bound {
+                    if dreg < 0 {
+                        self.set_flag(Flags::Negative, true);
+                    } else if dreg > upper_bound {
+                        self.set_flag(Flags::Negative, false);
+                    }
+                    self.exception(Exceptions::ChkInstruction as u8, false)?;
+                }
+            },
             Instruction::CLR(target, size) => {
                 self.set_target_value(target, 0, size, Used::Once)?;
                 // Clear flags except Zero flag
@@ -652,8 +664,24 @@ impl M68k {
                 self.set_compare_flags(result, size, carry, overflow);
                 self.set_flag(Flags::Extend, carry);
             },
-            //Instruction::NEGX(Target, Size) => {
-            //},
+            Instruction::NEGX(dest, size) => {
+                let existing = self.get_target_value(dest, size, Used::Twice)?;
+                let extend = self.get_flag(Flags::Extend) as u32;
+                let (result1, carry1) = overflowing_sub_sized(0, existing, size);
+                let (result2, carry2) = overflowing_sub_sized(result1, extend, size);
+                let overflow = get_sub_overflow(0, existing, result2, size);
+
+                // Handle flags
+                let zero = self.get_flag(Flags::Zero);
+                self.set_compare_flags(result2, size, carry1 || carry2, overflow);
+                if self.get_flag(Flags::Zero) {
+                    // NEGX can only clear the zero flag, so if it's set, restore it to whatever it was before
+                    self.set_flag(Flags::Zero, zero);
+                }
+                self.set_flag(Flags::Extend, carry1 || carry2);
+
+                self.set_target_value(dest, result2, size, Used::Twice)?;
+            },
             Instruction::NOP => { },
             Instruction::NOT(target, size) => {
                 let mut value = self.get_target_value(target, size, Used::Twice)?;
diff --git a/tests/harte_tests/latest.txt b/tests/harte_tests/latest.txt
index 789a15b..80aaf4f 100644
--- a/tests/harte_tests/latest.txt
+++ b/tests/harte_tests/latest.txt
@@ -1,4 +1,4 @@
-Last run on 2022-09-12 at commit 5a55aa7f63834a24aae1db195a0d3aa7d8943fb9
+Last run on 2022-09-12 at commit 9ff528c4638b7b5757d110ba87c10ab60aa33557
 
 ABCD.json completed: 301 passed, 7764 FAILED
 ADD.b.json completed, all passed!
@@ -26,7 +26,7 @@ BSET.json completed, all passed!
 BSR.json completed: 4085 passed, 3980 FAILED
 BTST.json completed: 8052 passed, 13 FAILED
 Bcc.json completed: 5865 passed, 2200 FAILED
-CHK.json completed: 0 passed, 8065 FAILED
+CHK.json completed: 7744 passed, 321 FAILED
 CLR.b.json completed, all passed!
 CLR.l.json completed: 6882 passed, 1183 FAILED
 CLR.w.json completed: 6862 passed, 1203 FAILED
@@ -77,9 +77,9 @@ NBCD.json completed: 0 passed, 8065 FAILED
 NEG.b.json completed, all passed!
 NEG.l.json completed: 7552 passed, 513 FAILED
 NEG.w.json completed: 7531 passed, 534 FAILED
-NEGX.b.json completed: 0 passed, 8065 FAILED
-NEGX.l.json completed: 0 passed, 8065 FAILED
-NEGX.w.json completed: 0 passed, 8065 FAILED
+NEGX.b.json completed, all passed!
+NEGX.l.json completed: 7520 passed, 545 FAILED
+NEGX.w.json completed: 7510 passed, 555 FAILED
 NOP.json completed, all passed!
 NOT.b.json completed, all passed!
 NOT.l.json completed: 7512 passed, 553 FAILED
@@ -125,5 +125,5 @@ TST.l.json completed, all passed!
 TST.w.json completed, all passed!
 UNLINK.json completed, all passed!
 
-passed: 860483, failed: 139577, total 86%
-completed in 16m 38s
+passed: 891322, failed: 108738, total 89%
+completed in 13m 52s
diff --git a/tests/harte_tests/previous.txt b/tests/harte_tests/previous.txt
index ba7e410..789a15b 100644
--- a/tests/harte_tests/previous.txt
+++ b/tests/harte_tests/previous.txt
@@ -1,4 +1,4 @@
-Last run on 2022-09-11 at commit 42bfabb7434fdff65a1ccacced82ddc6597ed835
+Last run on 2022-09-12 at commit 5a55aa7f63834a24aae1db195a0d3aa7d8943fb9
 
 ABCD.json completed: 301 passed, 7764 FAILED
 ADD.b.json completed, all passed!