diff --git a/src/SIL.Machine/FiniteState/Fst.cs b/src/SIL.Machine/FiniteState/Fst.cs
index fbec0291e..f56d8f86d 100644
--- a/src/SIL.Machine/FiniteState/Fst.cs
+++ b/src/SIL.Machine/FiniteState/Fst.cs
@@ -368,7 +368,7 @@ out IEnumerable<FstResult<TData, TOffset>> results
             int annIndex = traversalMethod.Annotations.IndexOf(start);
 
             var initAnns = new HashSet<int>();
-            while (annIndex < traversalMethod.Annotations.Count)
+            while (annIndex < traversalMethod.Annotations.Count && annIndex > -1)
             {
                 var initRegisters = new Register<TOffset>[_registerCount, 2];