diff --git a/third_party/blink/renderer/platform/fonts/shaping/shape_result_view.cc b/third_party/blink/renderer/platform/fonts/shaping/shape_result_view.cc
index a21a16a12a9c9..753d97911d07e 100644
--- a/third_party/blink/renderer/platform/fonts/shaping/shape_result_view.cc
+++ b/third_party/blink/renderer/platform/fonts/shaping/shape_result_view.cc
@@ -548,6 +548,15 @@ float ShapeResultView::ForEachGraphemeClusters(const StringView& text,
         continue;
       }
 
+      if (current_character_index >= text.length()) [[unlikely]] {
+        // TODO(crbug.com/1147011): This should not happen, but crash logs
+        // indicate that |character_index| can exceed |num_characters_|.
+        // See also crbug.com/1286882. Unlike ForEachGlyphImpl, the LTR
+        // branch above has no upper bound, so guard here before the
+        // callback indexes into |text|.
+        NOTREACHED();
+      }
+
       cluster_advance += glyph_data.advance.ToFloat();
 
       if (text.Is8Bit()) {