diff --git a/src/py65/devices/mpu6502.py b/src/py65/devices/mpu6502.py
index ab613e1..b2bb306 100644
--- a/src/py65/devices/mpu6502.py
+++ b/src/py65/devices/mpu6502.py
@@ -375,7 +375,7 @@ class MPU:
       else:
         self.p |= self.NEGATIVE
         data +=100
-      self.a = convert_to_bcd(data)
+      self.a = convert_to_bcd(data) # throws exception if result is over 99 decimal
     else:
       if self.p & self.CARRY:
         borrow = 0
diff --git a/src/py65/tests/devices/test_mpu6502.py b/src/py65/tests/devices/test_mpu6502.py
index ba54bab..c31bc34 100644
--- a/src/py65/tests/devices/test_mpu6502.py
+++ b/src/py65/tests/devices/test_mpu6502.py
@@ -333,6 +333,20 @@ class Common6502Tests:
     self.assertEquals(mpu.OVERFLOW, mpu.p & mpu.OVERFLOW)       
     self.assertEquals(0, mpu.p & mpu.ZERO)       
 
+  def test_adc_bcd_on_immediate_79_plus_00_carry_set(self):
+    mpu = self._make_mpu()
+    mpu.p |= mpu.DECIMAL
+    mpu.p |= mpu.CARRY
+    mpu.a = 0x79
+    self._write(mpu.memory, 0x0000, (0x69, 0x00)) #=> $0000 ADC #$00
+    mpu.step()
+    self.assertEquals(0x0002, mpu.pc)
+    self.assertEquals(0x80, mpu.a)
+    self.assertEquals(mpu.NEGATIVE, mpu.p & mpu.NEGATIVE)    
+    self.assertEquals(mpu.OVERFLOW, mpu.p & mpu.OVERFLOW)       
+    self.assertEquals(0, mpu.p & mpu.ZERO)       
+    self.assertEquals(0, mpu.p & mpu.CARRY)
+
   # ADC Absolute, X-Indexed
   
   def test_adc_bcd_off_abs_x_carry_clear_in_accumulator_zeroes(self):
@@ -4084,6 +4098,34 @@ class Common6502Tests:
     self.assertEquals(0, mpu.p & mpu.ZERO)  
     self.assertEquals(mpu.CARRY, mpu.CARRY)
 
+  def test_sbc_bcd_on_immediate_0a_minus_00_carry_set(self):
+    mpu = self._make_mpu()
+    mpu.p |= mpu.DECIMAL
+    mpu.p |= mpu.CARRY
+    mpu.a = 0x0a
+    self._write(mpu.memory, 0x0000, (0xe9, 0x00)) #=> $0000 SBC #$00
+    mpu.step()
+    self.assertEquals(0x0002, mpu.pc)
+    self.assertEquals(0x0a, mpu.a)
+    self.assertEquals(0, mpu.p & mpu.NEGATIVE)    
+    self.assertEquals(0, mpu.p & mpu.OVERFLOW)       
+    self.assertEquals(0, mpu.p & mpu.ZERO)       
+    self.assertEquals(mpu.CARRY, mpu.p & mpu.CARRY)
+
+  def test_sbc_bcd_on_immediate_9a_minus_00_carry_set(self):
+    mpu = self._make_mpu()
+    mpu.p |= mpu.DECIMAL
+    mpu.p |= mpu.CARRY
+    mpu.a = 0x9a
+    self._write(mpu.memory, 0x0000, (0xe9, 0x00)) #=> $0000 SBC #$00
+    mpu.step()
+    self.assertEquals(0x0002, mpu.pc)
+    self.assertEquals(0x9a, mpu.a)
+    self.assertEquals(mpu.NEGATIVE, mpu.p & mpu.NEGATIVE)    
+    self.assertEquals(0, mpu.p & mpu.OVERFLOW)       
+    self.assertEquals(0, mpu.p & mpu.ZERO)       
+    self.assertEquals(mpu.CARRY, mpu.p & mpu.CARRY)
+
   # SBC Absolute, X-Indexed
   
   def test_sbc_abs_x_all_zeros_and_no_borrow_is_zero(self):