diff --git a/src/macros.rs b/src/macros.rs
index ac77ed5..d1a4074 100644
--- a/src/macros.rs
+++ b/src/macros.rs
@@ -552,6 +552,7 @@ macro_rules! generate_element {
     );
 }
 
+#[cfg(test)]
 macro_rules! assert_size (
     ($t:ty, $sz:expr) => (
         assert_eq!(::std::mem::size_of::<$t>(), $sz);