diff --git a/rmp/tests/func/est.rs b/rmp/tests/func/est.rs
index 6f8f0e3f..f9421cb5 100644
--- a/rmp/tests/func/est.rs
+++ b/rmp/tests/func/est.rs
@@ -1,3 +1,5 @@
+#![cfg(feature = "std")]
+
 use rmp::Marker;
 use rmp::decode::MessageLen;
 use rmp::decode::LenError;