diff --git a/horrlang.py b/horrlang.py
index 29de523..6242455 100755
--- a/horrlang.py
+++ b/horrlang.py
@@ -61,7 +61,9 @@ class Machine:
         self.mem_ptr += self.get_integer()
 
     def O(self):
-        self.write(chr(self.mem[self.mem_ptr]))
+        char = self.mem[self.mem_ptr]
+        if char > 0 and char < 256:
+            self.write(chr(char))
 
     def I(self):
         self.mem[self.mem_ptr] = ord(self.read(1))
@@ -101,8 +103,9 @@ class Machine:
         while True:
             if self.mem[self.exc_ptr] == 0:
                 return
-            if self.mem[self.exc_ptr] <= 255:
-                control = chr(self.mem[self.exc_ptr])
+            char = self.mem[self.exc_ptr]
+            if char > 0 and char < 256:
+                control = chr(char)
                 if debug:
                     print control
                 if hasattr(self, control):