diff --git a/src/libstd/sys/windows/mod.rs b/src/libstd/sys/windows/mod.rs
index 6e3b48a8f642..5bb2a134533e 100644
--- a/src/libstd/sys/windows/mod.rs
+++ b/src/libstd/sys/windows/mod.rs
@@ -198,7 +198,7 @@ pub fn set_nonblocking(fd: sock_t, nb: bool) {
     if unsafe { c::ioctlsocket(fd, c::FIONBIO, &mut set) } != 0 {
         // The above function should not return an error unless we passed it
         // invalid parameters. Panic on errors.
-        Err(last_error()).unwrap();
+        panic!("set_nonblocking called with invalid parameters: {}", last_error());
     }
 }