diff --git a/src/simulator/machine.rs b/src/simulator/machine.rs
index 123b43b..9baf651 100644
--- a/src/simulator/machine.rs
+++ b/src/simulator/machine.rs
@@ -227,7 +227,6 @@ impl Machine {
 	}
 
 	pub fn raise_exception(&mut self, exception: ExceptionType, address : u64, system: &mut System) -> Result<MachineOk, MachineError>{
-
 		self.set_status(MachineStatus::SystemMode);
 		// Handle the interruption
 		match exception::call(exception, self, system) {
@@ -235,7 +234,7 @@ impl Machine {
 				self.set_status(MachineStatus::UserMode);
 				return Ok(MachineOk::Shutdown);
 			}
-			_ => ()
+			_ => Err(format!("Syscall {:?} invalid or not implemented", exception))?
 		} // todo: return error if the syscall code is invalid 
 		self.set_status(MachineStatus::UserMode);
 		Ok(MachineOk::Ok)
@@ -251,7 +250,7 @@ impl Machine {
 			match self.one_instruction(system) {
 				Ok(MachineOk::Ok) => println!("hello"),
 				Ok(MachineOk::Shutdown) => break,
-				Err(e) => { if e.to_string().contains("System") { break; } panic!("FATAL at pc {} -> {}", self.pc, e) }
+				Err(e) => panic!("FATAL at pc {} -> {}", self.pc, e)
 			}
 			self.write_int_register(0, 0); // In case an instruction write on register 0
 		}