diff --git a/beacon_node/beacon_chain/test_harness/src/lib.rs b/beacon_node/beacon_chain/test_harness/src/lib.rs
index 0703fd4a5..e93fa7003 100644
--- a/beacon_node/beacon_chain/test_harness/src/lib.rs
+++ b/beacon_node/beacon_chain/test_harness/src/lib.rs
@@ -8,7 +8,7 @@
 //! producing blocks and attestations.
 //!
 //! Example:
-//! ```
+//! ```rust,no_run
 //! use test_harness::BeaconChainHarness;
 //! use types::ChainSpec;
 //!