diff --git a/src/SIL.Machine/Utils/EnumerableExtensions.cs b/src/SIL.Machine/Utils/EnumerableExtensions.cs
index 1c2fc72b0..8bab692e2 100644
--- a/src/SIL.Machine/Utils/EnumerableExtensions.cs
+++ b/src/SIL.Machine/Utils/EnumerableExtensions.cs
@@ -13,6 +13,8 @@ Func<IEnumerable<TSource>, TResult> selector
         {
             // ToList is necessary to avoid deferred execution
             List<IEnumerator<TSource>> enumerators = source.Select(seq => seq.GetEnumerator()).ToList();
+            if (enumerators.Count == 0)
+                yield break;
             try
             {
                 while (true)