diff --git a/src/flatcollections-array/FlatArray/FlatArrayExtensions/Extensions.ToFlatArray.FromArray.cs b/src/flatcollections-array/FlatArray/FlatArrayExtensions/Extensions.ToFlatArray.FromArray.cs
index c5b597f8..1e323670 100644
--- a/src/flatcollections-array/FlatArray/FlatArrayExtensions/Extensions.ToFlatArray.FromArray.cs
+++ b/src/flatcollections-array/FlatArray/FlatArrayExtensions/Extensions.ToFlatArray.FromArray.cs
@@ -7,4 +7,9 @@ partial class FlatArrayExtensions
     public static FlatArray<T> ToFlatArray<T>([AllowNull] this T[] source)
         =>
         FlatArray<T>.From(source);
+
+    // TODO: Add the tests and make public
+    internal static FlatArray<T> ToFlatArray<T>([AllowNull] this T[] source, int start, int length)
+        =>
+        FlatArray<T>.InternalFromArrayChecked(source, start, length);
 }
diff --git a/src/flatcollections-array/FlatArray/FlatArrayExtensions/Extensions.ToFlatArray.FromFlatArray.cs b/src/flatcollections-array/FlatArray/FlatArrayExtensions/Extensions.ToFlatArray.FromFlatArray.cs
index 3c5ac4ff..ce668b80 100644
--- a/src/flatcollections-array/FlatArray/FlatArrayExtensions/Extensions.ToFlatArray.FromFlatArray.cs
+++ b/src/flatcollections-array/FlatArray/FlatArrayExtensions/Extensions.ToFlatArray.FromFlatArray.cs
@@ -6,7 +6,17 @@ public static FlatArray<T> ToFlatArray<T>(this FlatArray<T> source)
         =>
         FlatArray<T>.From(source);
 
+    // TODO: Add the tests and make public
+    internal static FlatArray<T> ToFlatArray<T>(this FlatArray<T> source, int start, int length)
+        =>
+        FlatArray<T>.InternalFromFlatArrayChecked(source, start, length);
+
     public static FlatArray<T> ToFlatArray<T>(this FlatArray<T>? source)
         =>
         FlatArray<T>.From(source);
+
+    // TODO: Add the tests and make public
+    internal static FlatArray<T> ToFlatArray<T>(this FlatArray<T>? source, int start, int length)
+        =>
+        FlatArray<T>.InternalFromFlatArrayChecked(source.GetValueOrDefault(), start, length);
 }
diff --git a/src/flatcollections-array/FlatArray/FlatArrayExtensions/Extensions.ToFlatArray.FromImmutableArray.cs b/src/flatcollections-array/FlatArray/FlatArrayExtensions/Extensions.ToFlatArray.FromImmutableArray.cs
index 542e7034..f6c5c853 100644
--- a/src/flatcollections-array/FlatArray/FlatArrayExtensions/Extensions.ToFlatArray.FromImmutableArray.cs
+++ b/src/flatcollections-array/FlatArray/FlatArrayExtensions/Extensions.ToFlatArray.FromImmutableArray.cs
@@ -8,7 +8,17 @@ public static FlatArray<T> ToFlatArray<T>(this ImmutableArray<T> source)
         =>
         FlatArray<T>.From(source);
 
+    // TODO: Add the tests and make public
+    internal static FlatArray<T> ToFlatArray<T>(this ImmutableArray<T> source, int start, int length)
+        =>
+        FlatArray<T>.InternalFromImmutableArrayChecked(source, start, length);
+
     public static FlatArray<T> ToFlatArray<T>(this ImmutableArray<T>? source)
         =>
         FlatArray<T>.From(source);
+
+    // TODO: Add the tests and make public
+    internal static FlatArray<T> ToFlatArray<T>(this ImmutableArray<T>? source, int start, int length)
+        =>
+        FlatArray<T>.InternalFromImmutableArrayChecked(source.GetValueOrDefault(), start, length);
 }
diff --git a/src/flatcollections-array/FlatArray/FlatArrayExtensions/Extensions.ToFlatArray.FromList.cs b/src/flatcollections-array/FlatArray/FlatArrayExtensions/Extensions.ToFlatArray.FromList.cs
index c842baf5..b695d7e6 100644
--- a/src/flatcollections-array/FlatArray/FlatArrayExtensions/Extensions.ToFlatArray.FromList.cs
+++ b/src/flatcollections-array/FlatArray/FlatArrayExtensions/Extensions.ToFlatArray.FromList.cs
@@ -8,4 +8,9 @@ partial class FlatArrayExtensions
     public static FlatArray<T> ToFlatArray<T>([AllowNull] this List<T> source)
         =>
         FlatArray<T>.From(source);
+
+    // TODO: Add the tests and make public
+    internal static FlatArray<T> ToFlatArray<T>([AllowNull] this List<T> source, int start, int length)
+        =>
+        FlatArray<T>.InternalFromListChecked(source, start, length);
 }