diff --git a/src/hb-subset-cff-common.cc b/src/hb-subset-cff-common.cc
index aa5d27b36..223c6a821 100644
--- a/src/hb-subset-cff-common.cc
+++ b/src/hb-subset-cff-common.cc
@@ -226,7 +226,7 @@ hb_serialize_cff_fdselect (hb_serialize_context_t *c,
 						fdselect_ranges);
 
     default:
-      assert(false);
+      return_trace (false);
   }
 
   return_trace (true);
diff --git a/test/fuzzing/fonts/clusterfuzz-testcase-minimized-hb-subset-fuzzer-5680398559870976 b/test/fuzzing/fonts/clusterfuzz-testcase-minimized-hb-subset-fuzzer-5680398559870976
new file mode 100644
index 000000000..5c7b6b50b
Binary files /dev/null and b/test/fuzzing/fonts/clusterfuzz-testcase-minimized-hb-subset-fuzzer-5680398559870976 differ