diff --git a/src/libtest/lib.rs b/src/libtest/lib.rs
index 30c34746c34e4..39a9ac8569ad0 100644
--- a/src/libtest/lib.rs
+++ b/src/libtest/lib.rs
@@ -439,6 +439,8 @@ pub fn parse_opts(args: &[String]) -> Option<OptRes> {
     let test_threads = match matches.opt_str("test-threads") {
         Some(n_str) =>
             match n_str.parse::<usize>() {
+                Ok(0) =>
+                    return Some(Err(format!("argument for --test-threads must not be 0"))),
                 Ok(n) => Some(n),
                 Err(e) =>
                     return Some(Err(format!("argument for --test-threads must be a number > 0 \