diff --git a/src/hru.rs b/src/hru.rs
index 1e57be4..2eae2ed 100644
--- a/src/hru.rs
+++ b/src/hru.rs
@@ -25,28 +25,34 @@ use std::{
 
 extern crate sysexits;
 
-use sysexits::EX_DATAERR;
+use sysexits::{ EX_DATAERR, EX_SOFTWARE };
 
-fn convert(input: u64) -> (f64, u32) {
+fn convert(input: u128) -> Result<(f64, u32), String> {
 	let list: Vec<u32> = vec![3, 6, 9, 12, 15, 18, 21, 24, 27, 30];
 	let mut out = (0.0, 0_u32);
 
-	if input < 1000 { return (input as f64, 0); }
+	if input < 1000 { return Ok((input as f64, 0)); }
 
 	for n in list {
-		let c = 10_u64.pow(n);
+		let c = match 10_u128.checked_pow(n) {
+			Some(c) => c,
+			None => {
+				return Err(format!("10^{}: Integer overflow.", n.to_string()));
+			},
+		};
+
 		match c.cmp(&input) {
 			Ordering::Less => {
 				out = (input as f64 / c as f64, n);
 			},
 			Ordering::Equal => {
-				return (input as f64 / c as f64, n);
+				return Ok((input as f64 / c as f64, n));
 			},
 			Ordering::Greater => {},
 		};
 	}
 
-	out
+	Ok(out)
 }
 
 fn main() -> ExitCode {
@@ -55,7 +61,7 @@ fn main() -> ExitCode {
 	while let Ok(_) = stdin().read_line(&mut buf) {
 		if buf.is_empty() { return ExitCode::SUCCESS; }
 
-		let n: u64 = match buf.trim().parse() {
+		let n: u128 = match buf.trim().parse() {
 			Ok(f) => {
 				buf.clear();
 				f
@@ -66,7 +72,13 @@ fn main() -> ExitCode {
 			},
 		};
 
-		let (number, prefix) = convert(n);
+		let (number, prefix) = match convert(n) {
+			Ok(x) => x,
+			Err(err) => {
+				eprintln!("{}: {}", argv[0], err);
+				return ExitCode::from(EX_SOFTWARE as u8);
+			},
+		};
 
 		let si_prefix = format!("{}B", match prefix {
 			3 => "K",