diff --git a/TODO.txt b/TODO.txt
index dd2b5c3..bf19853 100644
--- a/TODO.txt
+++ b/TODO.txt
@@ -3,5 +3,4 @@ Instructions needing unit tests:
   cmp
   cpx
   cpy
-  dec
   sbc
diff --git a/mpu.py b/mpu.py
index e4feda9..a43ebe0 100644
--- a/mpu.py
+++ b/mpu.py
@@ -370,9 +370,9 @@ class MPU:
     addr = x()
     tbyte = self.ByteAt(addr)
     self.flags &= ~(self.ZERO + self.NEGATIVE)
-    tbyte -= 1
+    tbyte = (tbyte - 1) & 0xFF
     if tbyte:
-      self.flags |= self.tbyte & 128
+      self.flags |= tbyte & self.NEGATIVE
     else:
       self.flags |= self.ZERO
     self.RAM[addr] = tbyte
@@ -1001,7 +1001,7 @@ class MPU:
     self.pc+=2
 
   def ide(self):
-    self.opDECR(AbsoluteXAddr)
+    self.opDECR(self.AbsoluteXAddr)
     self.pc+=2
 
   def ie0(self):
diff --git a/mpu_test.py b/mpu_test.py
index aa83441..6297422 100644
--- a/mpu_test.py
+++ b/mpu_test.py
@@ -1223,6 +1223,138 @@ class MPUTests(unittest.TestCase):
     mpu.step()
     self.assertEquals(0x0001, mpu.pc)
     self.assertEquals(0, mpu.flags & mpu.OVERFLOW)
+
+  # DEC Absolute
+  
+  def test_dec_abs_decrements_memory(self):
+    mpu = MPU()
+    mpu.memory[0x0000:0x0002] = (0xCE, 0xCD, 0xAB) #=> DEC 0xABCD
+    mpu.memory[0xABCD] = 0x10
+    mpu.step()
+    self.assertEquals(0x0003, mpu.pc)
+    self.assertEquals(0x0F, mpu.memory[0xABCD])
+    self.assertEquals(0, mpu.flags & mpu.NEGATIVE)
+    self.assertEquals(0, mpu.flags & mpu.ZERO)
+
+  def test_dec_abs_below_00_rolls_over_and_sets_negative_flag(self):
+    mpu = MPU()
+    mpu.memory[0x0000:0x0002] = (0xCE, 0xCD, 0xAB) #=> DEC 0xABCD
+    mpu.memory[0xABCD] = 0x00
+    mpu.step()
+    self.assertEquals(0x0003, mpu.pc)
+    self.assertEquals(0xFF, mpu.memory[0xABCD])
+    self.assertEquals(0, mpu.flags & mpu.ZERO)        
+    self.assertEquals(mpu.NEGATIVE, mpu.flags & mpu.NEGATIVE)        
+
+  def test_dec_abs_sets_zero_flag_when_decrementing_to_zero(self):
+    mpu = MPU()
+    mpu.memory[0x0000:0x0002] = (0xCE, 0xCD, 0xAB) #=> DEC 0xABCD
+    mpu.memory[0xABCD] = 0x01
+    mpu.step()
+    self.assertEquals(0x0003, mpu.pc)
+    self.assertEquals(0x00, mpu.memory[0xABCD])
+    self.assertEquals(mpu.ZERO, mpu.flags & mpu.ZERO)
+    self.assertEquals(0, mpu.flags & mpu.NEGATIVE)      
+
+  # DEC Zero Page
+
+  def test_dec_zp_decrements_memory(self):
+    mpu = MPU()
+    mpu.memory[0x0000:0x0001] = (0xC6, 0x10) #=> DEC 0x0010
+    mpu.memory[0x0010] = 0x10
+    mpu.step()
+    self.assertEquals(0x0002, mpu.pc)
+    self.assertEquals(0x0F, mpu.memory[0x0010])
+    self.assertEquals(0, mpu.flags & mpu.NEGATIVE)
+    self.assertEquals(0, mpu.flags & mpu.ZERO)
+
+  def test_dec_zp_below_00_rolls_over_and_sets_negative_flag(self):
+    mpu = MPU()
+    mpu.memory[0x0000:0x0001] = (0xC6, 0x10) #=> DEC 0x0010
+    mpu.memory[0x0010] = 0x00
+    mpu.step()
+    self.assertEquals(0x0002, mpu.pc)
+    self.assertEquals(0xFF, mpu.memory[0x0010])
+    self.assertEquals(0, mpu.flags & mpu.ZERO)        
+    self.assertEquals(mpu.NEGATIVE, mpu.flags & mpu.NEGATIVE)        
+
+  def test_dec_zp_sets_zero_flag_when_decrementing_to_zero(self):
+    mpu = MPU()
+    mpu.memory[0x0000:0x0001] = (0xC6, 0x10) #=> DEC 0x0010
+    mpu.memory[0x0010] = 0x01
+    mpu.step()
+    self.assertEquals(0x0002, mpu.pc)
+    self.assertEquals(0x00, mpu.memory[0x0010])
+    self.assertEquals(mpu.ZERO, mpu.flags & mpu.ZERO)
+    self.assertEquals(0, mpu.flags & mpu.NEGATIVE)      
+
+  # DEC Absolute, X-Indexed
+  
+  def test_dec_abs_x_decrements_memory(self):
+    mpu = MPU()
+    mpu.memory[0x0000:0x0002] = (0xDE, 0xCD, 0xAB) #=> DEC 0xABCD,X
+    mpu.x = 0x03
+    mpu.memory[0xABCD + mpu.x] = 0x10
+    mpu.step()
+    self.assertEquals(0x0003, mpu.pc)
+    self.assertEquals(0x0F, mpu.memory[0xABCD + mpu.x])
+    self.assertEquals(0, mpu.flags & mpu.NEGATIVE)
+    self.assertEquals(0, mpu.flags & mpu.ZERO)
+
+  def test_dec_abs_x_below_00_rolls_over_and_sets_negative_flag(self):
+    mpu = MPU()
+    mpu.memory[0x0000:0x0002] = (0xDE, 0xCD, 0xAB) #=> DEC 0xABCD,X
+    mpu.memory[0xABCD + mpu.x] = 0x00
+    mpu.step()
+    self.assertEquals(0x0003, mpu.pc)
+    self.assertEquals(0xFF, mpu.memory[0xABCD + mpu.x])
+    self.assertEquals(0, mpu.flags & mpu.ZERO)        
+    self.assertEquals(mpu.NEGATIVE, mpu.flags & mpu.NEGATIVE)        
+
+  def test_dec_abs_x_sets_zero_flag_when_decrementing_to_zero(self):
+    mpu = MPU()
+    mpu.memory[0x0000:0x0002] = (0xDE, 0xCD, 0xAB) #=> DEC 0xABCD,X
+    mpu.memory[0xABCD + mpu.x] = 0x01
+    mpu.step()
+    self.assertEquals(0x0003, mpu.pc)
+    self.assertEquals(0x00, mpu.memory[0xABCD + mpu.x])
+    self.assertEquals(mpu.ZERO, mpu.flags & mpu.ZERO)
+    self.assertEquals(0, mpu.flags & mpu.NEGATIVE)      
+
+  # DEC Zero Page, X-Indexed
+
+  def test_dec_zp_x_decrements_memory(self):
+    mpu = MPU()
+    mpu.memory[0x0000:0x0001] = (0xD6, 0x10) #=> DEC 0x0010,X
+    mpu.x = 0x03
+    mpu.memory[0x0010 + mpu.x] = 0x10
+    mpu.step()
+    self.assertEquals(0x0002, mpu.pc)
+    self.assertEquals(0x0F, mpu.memory[0x0010 + mpu.x])
+    self.assertEquals(0, mpu.flags & mpu.NEGATIVE)
+    self.assertEquals(0, mpu.flags & mpu.ZERO)
+
+  def test_dec_zp_x_below_00_rolls_over_and_sets_negative_flag(self):
+    mpu = MPU()
+    mpu.memory[0x0000:0x0001] = (0xD6, 0x10) #=> DEC 0x0010,X
+    mpu.x = 0x03
+    mpu.memory[0x0010 + mpu.x] = 0x00
+    mpu.step()
+    self.assertEquals(0x0002, mpu.pc)
+    self.assertEquals(0xFF, mpu.memory[0x0010 + mpu.x])
+    self.assertEquals(0, mpu.flags & mpu.ZERO)        
+    self.assertEquals(mpu.NEGATIVE, mpu.flags & mpu.NEGATIVE)        
+
+  def test_dec_zp_x_sets_zero_flag_when_decrementing_to_zero(self):
+    mpu = MPU()
+    mpu.memory[0x0000:0x0001] = (0xD6, 0x10) #=> DEC 0x0010,X
+    mpu.x = 0x03
+    mpu.memory[0x0010 + mpu.x] = 0x01
+    mpu.step()
+    self.assertEquals(0x0002, mpu.pc)
+    self.assertEquals(0x00, mpu.memory[0x0010 + mpu.x])
+    self.assertEquals(mpu.ZERO, mpu.flags & mpu.ZERO)
+    self.assertEquals(0, mpu.flags & mpu.NEGATIVE)      
         
   # DEX
   
@@ -1233,6 +1365,8 @@ class MPUTests(unittest.TestCase):
     mpu.step()
     self.assertEquals(0x0001, mpu.pc)
     self.assertEquals(0x0F, mpu.x)
+    self.assertEquals(0, mpu.flags & mpu.NEGATIVE)
+    self.assertEquals(0, mpu.flags & mpu.ZERO)
       
   def test_dex_below_00_rolls_over_and_sets_negative_flag(self):
     mpu = MPU()
@@ -1242,7 +1376,8 @@ class MPUTests(unittest.TestCase):
     self.assertEquals(0x0001, mpu.pc)
     self.assertEquals(0xFF, mpu.x)
     self.assertEquals(mpu.NEGATIVE, mpu.flags & mpu.NEGATIVE)
-    
+    self.assertEquals(0, mpu.flags & mpu.ZERO)
+        
   def test_dex_sets_zero_flag_when_decrementing_to_zero(self):
     mpu = MPU()
     mpu.x = 0x01
@@ -1251,6 +1386,7 @@ class MPUTests(unittest.TestCase):
     self.assertEquals(0x0001, mpu.pc)
     self.assertEquals(0x00, mpu.x)
     self.assertEquals(mpu.ZERO, mpu.flags & mpu.ZERO)
+    self.assertEquals(0, mpu.flags & mpu.NEGATIVE)
     
   # DEY
   
@@ -1261,6 +1397,8 @@ class MPUTests(unittest.TestCase):
     mpu.step()
     self.assertEquals(0x0001, mpu.pc)
     self.assertEquals(0x0F, mpu.y)
+    self.assertEquals(0, mpu.flags & mpu.NEGATIVE)
+    self.assertEquals(0, mpu.flags & mpu.ZERO)
       
   def test_dey_below_00_rolls_over_and_sets_negative_flag(self):
     mpu = MPU()