diff --git a/consensus/proto_array/src/error.rs b/consensus/proto_array/src/error.rs
index 04e747f5f6..bb5eea569d 100644
--- a/consensus/proto_array/src/error.rs
+++ b/consensus/proto_array/src/error.rs
@@ -60,6 +60,7 @@ pub enum Error {
     BrokenBlock {
         block_root: Hash256,
     },
+    NoViableChildren,
 }
 
 impl From<ArithError> for Error {
diff --git a/consensus/proto_array/src/proto_array.rs b/consensus/proto_array/src/proto_array.rs
index 3f8db8d1fb..e3671eef7d 100644
--- a/consensus/proto_array/src/proto_array.rs
+++ b/consensus/proto_array/src/proto_array.rs
@@ -1338,7 +1338,7 @@ impl ProtoArray {
                     (*weight, child.root, *payload_status_tiebreaker)
                 })
                 .map(|(child, _, _)| child)
-                .expect("children is non-empty");
+                .ok_or(Error::NoViableChildren)?;
         }
     }