diff --git a/src/core/include/megbrain/common.h b/src/core/include/megbrain/common.h
index af32f04efbb0c963490884c95234efe8a8dc2745..49f5d930491c35877172a21ee2d2e60263bba391 100644
--- a/src/core/include/megbrain/common.h
+++ b/src/core/include/megbrain/common.h
@@ -48,6 +48,13 @@ namespace mgb {
 //! warn if result of a function is not used
 #define MGB_WARN_UNUSED_RESULT __attribute__((warn_unused_result))
 
+#if __cplusplus >= 201703L || __clang_major__ >= 4
+#define MGB_FALLTHRU [[fallthrough]];
+#elif __GNUC__ >= 7
+#define MGB_FALLTHRU __attribute__((fallthrough));
+#else
+#define MGB_FALLTHRU
+#endif
 
 /* ================ exception and assertion ================  */
 
diff --git a/src/serialization/impl/serializer.cpp b/src/serialization/impl/serializer.cpp
index e5375d72348b3b61e7fbae8e8f60663eadf647e8..76d1495f21771ddd312eb269e4cfd89b139a824f 100644
--- a/src/serialization/impl/serializer.cpp
+++ b/src/serialization/impl/serializer.cpp
@@ -53,10 +53,11 @@ bool GraphDumper::should_remove_in_dump(cg::OperatorNodeBase *opr) {
 std::unique_ptr<GraphDumper> GraphDumper::make(std::unique_ptr<OutputFile> file,
                                                GraphDumpFormat format) {
     switch (format) {
-#if MGB_ENABLE_FBS_SERIALIZATION
         case GraphDumpFormat::FLATBUFFERS:
+#if MGB_ENABLE_FBS_SERIALIZATION
             return make_fbs_dumper(std::move(file));
 #endif
+        MGB_FALLTHRU
         default:
             mgb_throw(SerializationError,
                       "unsupported serialization format requested");
@@ -66,10 +67,11 @@ std::unique_ptr<GraphDumper> GraphDumper::make(std::unique_ptr<OutputFile> file,
 
 std::unique_ptr<GraphLoader> GraphLoader::make(std::unique_ptr<InputFile> file, GraphDumpFormat format) {
     switch (format) {
-#if MGB_ENABLE_FBS_SERIALIZATION
         case GraphDumpFormat::FLATBUFFERS:
+#if MGB_ENABLE_FBS_SERIALIZATION
             return make_fbs_loader(std::move(file));
 #endif
+        MGB_FALLTHRU
         default:
             mgb_throw(SerializationError,
                       "unsupported serialization format requested");
diff --git a/src/serialization/include/megbrain/serialization/opr_load_dump.h b/src/serialization/include/megbrain/serialization/opr_load_dump.h
index 7d8f4f5f66461d284c61da2afc400ed145a69842..84258ce2b5da135f6a283a2f2bef20a4ead43a3f 100644
--- a/src/serialization/include/megbrain/serialization/opr_load_dump.h
+++ b/src/serialization/include/megbrain/serialization/opr_load_dump.h
@@ -29,9 +29,7 @@ struct OperatorParamTraits;
 
 enum class SerializationFormat {
     RAW_POD,
-#if MGB_ENABLE_FBS_SERIALIZATION
     FLATBUFFERS,
-#endif
 };
 
 //! context for serializing a single operator
@@ -162,12 +160,12 @@ void OprDumpContext::write_param(const Param& p) {
         case SerializationFormat::RAW_POD:
             static_cast<OprDumpContextRawPOD*>(this)->write_param(p);
             break;
-#if MGB_ENABLE_FBS_SERIALIZATION
         case SerializationFormat::FLATBUFFERS:
+#if MGB_ENABLE_FBS_SERIALIZATION
             static_cast<OprDumpContextFlatBuffers*>(this)->write_param(
                     p, fbs::SupportFlatBuffersSerialization<Param>{});
-            break;
 #endif
+            break;
     }
 }
 
@@ -322,11 +320,13 @@ Param OprLoadContext::read_param() {
         case SerializationFormat::RAW_POD:
             return static_cast<OprLoadContextRawPOD*>(this)
                     ->read_param<Param>();
-#if MGB_ENABLE_FBS_SERIALIZATION
         case SerializationFormat::FLATBUFFERS:
+#if MGB_ENABLE_FBS_SERIALIZATION
             return static_cast<OprLoadContextFlatBuffers*>(this)
                     ->read_param<Param>(
                             fbs::SupportFlatBuffersSerialization<Param>{});
+#else
+            mgb_trap();
 #endif
     }
     mgb_assert(0);