diff --git a/src/interpreter/__interpreter.py b/src/interpreter/__interpreter.py
index fde294d..735a925 100644
--- a/src/interpreter/__interpreter.py
+++ b/src/interpreter/__interpreter.py
@@ -7,13 +7,20 @@ from colorama import Fore, Style, Back
 
 from .util import hexdump
 
-Operation: TypeAlias = str | int
+Operation: TypeAlias = int
 Subroutine: TypeAlias = Callable
 
 OPCODE_HEADER = "__interpreter__opcode"
+OPCODE_ERROR_TYPE_CHECK = f"Opcodes must be of type f{int}."
+OPCODE_ERROR_REUSE = "Opcode {opcode} has already been used."
+OPCODE_ERROR_ILLEGAL = (
+    "Opcode {opcode} cannot be found, has it been registered correct?"
+)
 
 
 def opcode(opcode: Operation):
+    assert type(opcode) == Operation, OPCODE_ERROR_TYPE_CHECK
+
     def _helper(func: Callable):
         setattr(func, OPCODE_HEADER, opcode)
         return func
@@ -36,7 +43,7 @@ class Memory:
 
     def __setitem__(self, idx, value) -> None:
         self.__memory[idx] = value
-    
+
     def dump(self):
         return self.__memory
 
@@ -45,24 +52,36 @@ class Interpreter:
     def __init__(self, bits=8, memsize=None) -> None:
         self.__bits = bits
 
+        self.__max_cpu_instructions = 2**self.__bits
         self.__memory_max_size = 2**self.__bits
         self.__memory_size = min(memsize or 2**bits, self.__memory_max_size)
         self._memory: Memory = Memory(self.__memory_size)
         self._registers: Registers = Registers()
 
-        self.__operations: dict[Operation, Subroutine] = dict()
+        self.__operations: list[Subroutine | None] = [
+            None for _ in range(self.__max_cpu_instructions)
+        ]
         self.__init_opcodes()
 
     def __init_opcodes(self):
         for _, func in getmembers(self, lambda obj: hasattr(obj, OPCODE_HEADER)):
             opcode = getattr(func, OPCODE_HEADER)
+            assert self.__operations[opcode] is None, OPCODE_ERROR_REUSE.format(
+                opcode=opcode
+            )
+
             self.__operations[opcode] = func
 
     def run(self) -> None:
         try:
             # Keep running until you reach a null byte
             while (opcode := self._memory[self._registers.program_counter]) != 0:
-                self.__operations[opcode]()
+                subroutine = self.__operations[opcode]
+                assert subroutine is not None, OPCODE_ERROR_ILLEGAL.format(
+                    opcode=opcode
+                )
+
+                subroutine()
                 self._registers.program_counter += 1
         except Exception as e:
             self.dump()