diff --git a/src/hb-ot-shape-fallback.cc b/src/hb-ot-shape-fallback.cc
index 458c8eaa0..695f6b06a 100644
--- a/src/hb-ot-shape-fallback.cc
+++ b/src/hb-ot-shape-fallback.cc
@@ -473,6 +473,7 @@ _hb_ot_shape_fallback_kern (const hb_ot_shape_plan_t *plan,
       pos[idx].x_advance += kern1;
       pos[skippy_iter.idx].x_advance += kern2;
       pos[skippy_iter.idx].x_offset += kern2;
+      buffer->unsafe_to_break (idx, skippy_iter.idx + 1);
     }
 
     if (y_kern)
@@ -482,6 +483,7 @@ _hb_ot_shape_fallback_kern (const hb_ot_shape_plan_t *plan,
       pos[idx].y_advance += kern1;
       pos[skippy_iter.idx].y_advance += kern2;
       pos[skippy_iter.idx].y_offset += kern2;
+      buffer->unsafe_to_break (idx, skippy_iter.idx + 1);
     }
 
     idx = skippy_iter.idx;