diff --git a/third_party/harfbuzz/src/harfbuzz-arabic.c b/third_party/harfbuzz/src/harfbuzz-arabic.c
index 0609232..de3c1f4 100644
--- a/third_party/harfbuzz/src/harfbuzz-arabic.c
+++ b/third_party/harfbuzz/src/harfbuzz-arabic.c
@@ -1009,7 +1009,7 @@ static HB_Bool arabicSyriacOpenTypeShape(HB_ShaperItem *item, HB_Bool *ot_ok)
         ++l;
         ++properties;
     }
-    if (f + l < item->stringLength) {
+    if (f + l + item->item.pos < item->stringLength) {
         ++l;
     }
     getArabicProperties(uc+f, l, props);