diff --git a/src/graph/graph.hh b/src/graph/graph.hh
index 068095819..f81bed81e 100644
--- a/src/graph/graph.hh
+++ b/src/graph/graph.hh
@@ -290,7 +290,7 @@ struct graph_t
 	new_parents.set (id_map[_.first], _.second);
       }
 
-      if (new_parents.in_error ())
+      if (parents.in_error() || new_parents.in_error ())
         return false;
 
       parents = std::move (new_parents);
@@ -310,8 +310,15 @@ struct graph_t
       if (parents.has (old_index, &pv))
       {
         unsigned v = *pv;
-	parents.set (new_index, v);
+	if (!parents.set (new_index, v))
+          incoming_edges_ -= v;
 	parents.del (old_index);
+
+        if (incoming_edges_ == 1)
+	{
+	  single_parent = *parents.keys ();
+	  parents.reset ();
+	}
       }
     }
 
diff --git a/test/fuzzing/fonts/clusterfuzz-testcase-minimized-hb-repacker-fuzzer-6697168080338944 b/test/fuzzing/fonts/clusterfuzz-testcase-minimized-hb-repacker-fuzzer-6697168080338944
new file mode 100644
index 000000000..1859841d5
Binary files /dev/null and b/test/fuzzing/fonts/clusterfuzz-testcase-minimized-hb-repacker-fuzzer-6697168080338944 differ