diff --git a/hugr-core/src/builder.rs b/hugr-core/src/builder.rs
index 38a5334b3..a53811ba9 100644
--- a/hugr-core/src/builder.rs
+++ b/hugr-core/src/builder.rs
@@ -88,6 +88,7 @@
 //! ```
 use thiserror::Error;
 
+use crate::extension::simple_op::OpLoadError;
 use crate::extension::{SignatureError, TO_BE_INFERRED};
 use crate::hugr::ValidationError;
 use crate::ops::handle::{BasicBlockID, CfgID, ConditionalID, DfgID, FuncID, TailLoopID};
@@ -194,6 +195,10 @@ pub enum BuildError {
         #[source]
         error: BuilderWiringError,
     },
+
+    #[error("Failed to load an extension op: {0}")]
+    #[allow(missing_docs)]
+    ExtensionOp(#[from] OpLoadError),
 }
 
 #[derive(Debug, Clone, PartialEq, Error)]
diff --git a/hugr-core/src/extension/simple_op.rs b/hugr-core/src/extension/simple_op.rs
index 0bf1068a4..6906b40d7 100644
--- a/hugr-core/src/extension/simple_op.rs
+++ b/hugr-core/src/extension/simple_op.rs
@@ -17,7 +17,7 @@ use delegate::delegate;
 use thiserror::Error;
 
 /// Error loading operation.
-#[derive(Debug, Error, PartialEq)]
+#[derive(Debug, Error, PartialEq, Clone)]
 #[error("{0}")]
 #[allow(missing_docs)]
 #[non_exhaustive]