diff --git a/Makefile b/Makefile
index ef52a78..9d4261d 100644
--- a/Makefile
+++ b/Makefile
@@ -83,7 +83,7 @@ build/bin/intcmp: src/intcmp.c build
 
 .PHONY: rpn
 rpn: build/bin/rpn
-build/bin/rpn: src/rpn.rs build
+build/bin/rpn: src/rpn.rs build sysexits
 	$(RUSTC) $(RUSTFLAGS) -o $@ src/rpn.rs
 
 .PHONY: scrut
diff --git a/src/rpn.rs b/src/rpn.rs
index 6819ca1..7e7f948 100644
--- a/src/rpn.rs
+++ b/src/rpn.rs
@@ -52,6 +52,10 @@ use std::{
 
 use CalcType::{ Add, Divide, Multiply, Power, Subtract, Val };
 
+extern crate sysexits;
+
+use sysexits::EX_DATAERR;
+
 #[derive(Clone, Copy, PartialEq, PartialOrd, Debug)]
 /// enum CalcType is a type containing operations used in the calculator.
 enum CalcType {
@@ -156,7 +160,8 @@ fn eval(
 			Val(_) => {
 				return Err(
 					EvaluationError {
-						message: "Unexpected value in the operator stack.".to_string()
+						message: "Unexpected value in the operator stack."
+							.to_string()
 					}
 				)
 			},
@@ -173,21 +178,25 @@ fn round_precise(value: &f64, precision: usize) -> f64 {
 
 fn main() -> ExitCode {
 	let argv = args().collect::<Vec<String>>();
-	let stack = VecDeque::new();
+	let mut stack = VecDeque::new();
 	let mut buf = String::new();
 	let precision = (-f64::EPSILON.log10() * 0.999).ceil() as usize;
 	
 	if argv.get(1).is_none() {
 		while let Ok(_) = stdin().read_line(&mut buf) {
-			match eval(&buf.trim(), stack.clone()) {
+			match eval(&buf.trim(), stack) {
 				Ok(val) => {
-					let precise = round_precise(val.iter().last().unwrap(), precision);
+					stack = val.clone();
+					let precise = round_precise(
+						stack.iter().last().unwrap(),
+						precision,
+					);
 					println!("{}", precise.to_string());
 					buf.clear();
 				},
 				Err(err) => {
 					eprintln!("{}: {}", argv[0], err.message);
-					return ExitCode::from(1);
+					return ExitCode::from(EX_DATAERR as u8);
 				},
 			};
 		}
@@ -203,7 +212,7 @@ fn main() -> ExitCode {
 			Ok(val) => println!("{}", val.iter().last().unwrap().to_string()),
 			Err(err) => {
 				eprintln!("{}: {}", argv[0], err.message);
-				return ExitCode::from(1);
+				return ExitCode::from(EX_DATAERR as u8);
 			},
 		};
 	}