diff --git a/src/hb-aat-layout-morx-table.hh b/src/hb-aat-layout-morx-table.hh
index fd955b5b7..15686b657 100644
--- a/src/hb-aat-layout-morx-table.hh
+++ b/src/hb-aat-layout-morx-table.hh
@@ -330,7 +330,8 @@ struct ContextualSubtable
     unsigned int num_entries = 0;
     if (unlikely (!machine.sanitize (c, &num_entries))) return_trace (false);
 
-    if (!Types::extended) return_trace (true);
+    if (!Types::extended)
+      return_trace (substitutionTables.sanitize (c, this, 0));
 
     unsigned int num_lookups = 0;
 
diff --git a/test/fuzzing/fonts/clusterfuzz-testcase-minimized-hb-shape-fuzzer-5631444412530688 b/test/fuzzing/fonts/clusterfuzz-testcase-minimized-hb-shape-fuzzer-5631444412530688
new file mode 100644
index 000000000..25f7d697e
Binary files /dev/null and b/test/fuzzing/fonts/clusterfuzz-testcase-minimized-hb-shape-fuzzer-5631444412530688 differ