diff --git a/src/vm.py b/src/vm.py
index 9b86b06..b1b55dd 100644
--- a/src/vm.py
+++ b/src/vm.py
@@ -119,6 +119,11 @@ class VM:
         """
         Make one step (only step into)
         """
+        if self.pc.value * 4 > len(self.mem) - 4:
+            raise VMException(
+                    VMExceptionType.END_OF_MEM,
+                    self.pc.value
+                    )
         opcode = self.mem[self.pc.value * 4]
         opdesc = self._fetch_opcode_desc(opcode)
         args = self._parse_arguments(opdesc)
@@ -148,6 +153,11 @@ class VM:
             self.continue_()
 
     def _fetch_opcode_desc(self, opcode: int):
+        if not opcode in OPCODES:
+            raise VMException(
+                    VMExceptionType.INVALID_OPCODE,
+                    self.pc.value
+                    )
         return OPCODES[opcode]
     
     def _parse_arguments(self, opdesc: OpcodeDescription) -> tuple[int, ...]: