diff --git a/src/hb-aat-layout-trak-table.hh b/src/hb-aat-layout-trak-table.hh
index 4b4bc2ffe..16729d16f 100644
--- a/src/hb-aat-layout-trak-table.hh
+++ b/src/hb-aat-layout-trak-table.hh
@@ -136,7 +136,7 @@ struct TrackData
     /* TODO bfind() */
     hb_array_t<Fixed> size_table ((base+sizeTable).arrayZ, sizes);
     unsigned int size_index;
-    for (size_index = 0; size_index < sizes; size_index++)
+    for (size_index = 0; size_index < sizes - 1; size_index++)
       if (size_table[size_index].to_float () >= csspx)
         break;