diff --git a/processor/src/trace/utils.rs b/processor/src/trace/utils.rs
index 5e3bb6b6d2..75e85cffba 100644
--- a/processor/src/trace/utils.rs
+++ b/processor/src/trace/utils.rs
@@ -31,7 +31,14 @@ impl<'a> TraceFragment<'a> {
     }
 
     /// Returns the number of rows in this execution trace fragment.
+    ///
+    /// Returns `0` if the fragment has no columns (i.e., `data` is empty).
+    /// Otherwise, returns the length of the first column, which should be the same
+    /// as the length of all other columns.
     pub fn len(&self) -> usize {
+        if self.data.is_empty() {
+            return 0;
+        }
         self.data[0].len()
     }