diff --git a/src/sixtypical/compiler.py b/src/sixtypical/compiler.py
index 2ffabcd..11d2e9e 100644
--- a/src/sixtypical/compiler.py
+++ b/src/sixtypical/compiler.py
@@ -556,9 +556,11 @@ class Compiler(object):
 
         if instr.direction > 0:
             self.compile_inc(instr, instr.dest)
+            final = instr.final.succ()
         elif instr.direction < 0:
             self.compile_dec(instr, instr.dest)
-        self.compile_cmp(instr, instr.final, instr.dest)
+            final = instr.final.pred()
+        self.compile_cmp(instr, final, instr.dest)
         self.emitter.emit(BNE(Relative(top_label)))
 
     def compile_with_interrupts_off(self, instr):
diff --git a/src/sixtypical/model.py b/src/sixtypical/model.py
index 75f7a7f..30d5d54 100644
--- a/src/sixtypical/model.py
+++ b/src/sixtypical/model.py
@@ -296,6 +296,20 @@ class ConstantRef(Ref):
     def low_byte(self):
         return self.value & 255
 
+    def pred(self):
+        assert self.type == TYPE_BYTE
+        value = self.value - 1
+        while value < 0:
+            value += 256
+        return ConstantRef(self.type, value)
+
+    def succ(self):
+        assert self.type == TYPE_BYTE
+        value = self.value + 1
+        while value > 255:
+            value -= 256
+        return ConstantRef(self.type, value)
+
 
 REG_A = LocationRef(TYPE_BYTE, 'a')
 REG_X = LocationRef(TYPE_BYTE, 'x')