diff --git a/src/SixLabors.Fonts/TextLayout.cs b/src/SixLabors.Fonts/TextLayout.cs
index 6f5a4648..7cf6552f 100644
--- a/src/SixLabors.Fonts/TextLayout.cs
+++ b/src/SixLabors.Fonts/TextLayout.cs
@@ -825,6 +825,11 @@ private static void SubstituteBidiMirrors(FontMetrics fontMetrics, GlyphSubstitu
 
         // TODO: This only replaces certain glyphs. We should investigate the specification further.
         // https://www.unicode.org/reports/tr50/#vertical_alternates
+        if (collection.TextOptions.LayoutMode.IsHorizontal())
+        {
+            return;
+        }
+
         for (int i = 0; i < collection.Count; i++)
         {
             GlyphShapingData data = collection[i];