diff --git a/src/vm/instruction.rs b/src/vm/instruction.rs
index 92b0010..f3d3b9f 100644
--- a/src/vm/instruction.rs
+++ b/src/vm/instruction.rs
@@ -81,12 +81,12 @@ pub fn execute_instruction(vm: &mut VM, instr: u16) {
         OpCode::AND => op_and(vm, instr),
         OpCode::LDR => op_ldr(vm, instr),
         OpCode::STR => op_str(vm, instr),
-        OpCode::RTI => todo!("RTI"),
+        OpCode::RTI => unimplemented!("RTI (privilege violation)"),
         OpCode::NOT => op_not(vm, instr),
         OpCode::LDI => op_ldi(vm, instr),
         OpCode::STI => op_sti(vm, instr),
         OpCode::JMP => op_jmp(vm, instr),
-        OpCode::RES => todo!("RES"),
+        OpCode::RES => unimplemented!("RES (illegal instruction)"),
         OpCode::LEA => op_lea(vm, instr),
         OpCode::TRAP => op_trap(vm, instr),
         OpCode::NOOP => no_op(vm, instr),