diff --git a/src/main.rs b/src/main.rs
index 155efc0..6d0f7e5 100644
--- a/src/main.rs
+++ b/src/main.rs
@@ -58,7 +58,9 @@ fn lagrange_interpolate(src: &[(u8, u8)], raw_x: u8) -> u8 {
 		for (j, &(raw_xj, _)) in src.iter().enumerate() {
 			if i != j {
 				let xj = Gf256::from_byte(raw_xj);
-				lix = lix * (x - xj) / (xi - xj);
+				let delta = xi - xj;
+				assert!(delta.poly !=0, "Duplicate shares");
+				lix = lix * (x - xj) / delta;
 			}
 		}
 		sum = sum + lix * yi;
@@ -135,7 +137,7 @@ fn read_shares() -> IoResult<(u8, Vec<(u8,Vec<u8>)>)> {
 	let mut stdin = BufferedReader::new(stdio::stdin());
 	let mut opt_k_l: Option<(u8, usize)> = None;
 	let mut counter = 0u8;
-	let mut shares = Vec::new();
+	let mut shares: Vec<(u8,Vec<u8>)> = Vec::new();
 	for line in stdin.lines() {
 		let line = try!(line);
 		let parts: Vec<_> = line.split('-').collect();
@@ -167,13 +169,15 @@ fn read_shares() -> IoResult<(u8, Vec<(u8,Vec<u8>)>)> {
 		} else {
 			opt_k_l = Some((k,raw.len()));
 		}
-		shares.push((n, raw));
-		counter += 1;
-		if counter == k {
-			return Ok((k, shares));
+		if shares.iter().all(|s| s.0 != n) {
+			shares.push((n, raw));
+			counter += 1;
+			if counter == k {
+				return Ok((k, shares));
+			}
 		}
 	}
-	Err(other_io_err("No shares"))
+	Err(other_io_err("Not enough shares provided!"))
 }
 
 fn perform_decode() -> IoResult<()> {
@@ -213,6 +217,7 @@ fn main() {
 "The program secretshare is an implementation of Shamir's secret sharing scheme.\n\
  It is applied byte-wise within a finite field for arbitraty long secrets.\n");
 		println!("{}", opts.usage("Usage: secretshare [options]"));
+		println!("Input is read from STDIN and output is written to STDOUT.");
  		return;
 	}