diff --git a/src/SIL.Machine/Corpora/CorporaExtensions.cs b/src/SIL.Machine/Corpora/CorporaExtensions.cs
index 33186799..f5e1b4b1 100644
--- a/src/SIL.Machine/Corpora/CorporaExtensions.cs
+++ b/src/SIL.Machine/Corpora/CorporaExtensions.cs
@@ -544,20 +544,12 @@ public static ITextCorpus ChooseRandom(
             int seed
         )
         {
-            return new MergedTextCorpus(
-                new NParallelTextCorpus(corpora) { AllRows = allRows.ToArray() },
-                MergeRule.Random,
-                seed
-            );
+            return new MergedTextCorpus(corpora, allRows.ToArray(), MergeRule.Random, seed);
         }
 
         public static ITextCorpus ChooseFirst(this IEnumerable<ITextCorpus> corpora, IEnumerable<bool> allRows)
         {
-            return new MergedTextCorpus(
-                new NParallelTextCorpus(corpora) { AllRows = allRows.ToArray() },
-                MergeRule.First,
-                0
-            );
+            return new MergedTextCorpus(corpora, allRows.ToArray(), MergeRule.First, 0);
         }
 
         #endregion
diff --git a/src/SIL.Machine/Corpora/MergedTextCorpus.cs b/src/SIL.Machine/Corpora/MergedTextCorpus.cs
index 890f7e10..1bcbf822 100644
--- a/src/SIL.Machine/Corpora/MergedTextCorpus.cs
+++ b/src/SIL.Machine/Corpora/MergedTextCorpus.cs
@@ -13,9 +13,14 @@ public class MergedTextCorpus : TextCorpusBase
 
         private readonly Random _random;
 
-        public MergedTextCorpus(NParallelTextCorpus nParallelTextCorpus, MergeRule mergeRule, int seed)
+        public MergedTextCorpus(
+            IEnumerable<ITextCorpus> corpora,
+            IEnumerable<bool> allRows,
+            MergeRule mergeRule,
+            int seed
+        )
         {
-            _corpus = nParallelTextCorpus;
+            _corpus = new NParallelTextCorpus(corpora) { AllRows = allRows.ToList() };
             _mergeRule = mergeRule;
             _random = new Random(seed);
         }