diff --git a/src/libcore/str.rs b/src/libcore/str.rs
index 095605326c7f5..800e2dcc27893 100644
--- a/src/libcore/str.rs
+++ b/src/libcore/str.rs
@@ -562,7 +562,7 @@ enum Searcher {
 impl Searcher {
     fn new(haystack: &[u8], needle: &[u8]) -> Searcher {
         // FIXME: Tune this.
-        if needle.len() > haystack.len() - 20 {
+        if needle.len() + 20 > haystack.len() {
             Naive(NaiveSearcher::new())
         } else {
             let searcher = TwoWaySearcher::new(needle);
diff --git a/src/libcoretest/lib.rs b/src/libcoretest/lib.rs
index 3864321586ca6..7866d2f4a111c 100644
--- a/src/libcoretest/lib.rs
+++ b/src/libcoretest/lib.rs
@@ -29,4 +29,5 @@ mod ptr;
 mod raw;
 mod result;
 mod slice;
+mod str;
 mod tuple;
diff --git a/src/libcoretest/str.rs b/src/libcoretest/str.rs
new file mode 100644
index 0000000000000..bac8d509b1314
--- /dev/null
+++ b/src/libcoretest/str.rs
@@ -0,0 +1,14 @@
+// Copyright 2014 The Rust Project Developers. See the COPYRIGHT
+// file at the top-level directory of this distribution and at
+// http://rust-lang.org/COPYRIGHT.
+//
+// Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
+// http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
+// <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
+// option. This file may not be copied, modified, or distributed
+// except according to those terms.
+
+#[test]
+fn strslice_issue_16589() {
+    assert!("bananas".contains("nana"));
+}