diff --git a/src/core/impl/exception.cpp b/src/core/impl/exception.cpp
index 489be4f898c75631db6a3f96fa32eb27c48a3a7f..5e78054f89255cc5e57245543bbab0c109d4e264 100644
--- a/src/core/impl/exception.cpp
+++ b/src/core/impl/exception.cpp
@@ -35,15 +35,14 @@ namespace {
     MegDNNErrorHandler MegDNNErrorHandler::inst;
 }
 
-MegBrainError::MegBrainError(const std::string &msg):
-    m_msg(msg)
+void MegBrainError::init()
 {
     m_msg.append("\n");
 #if MGB_ENABLE_DEBUG_UTIL
     debug::backtrace(2).fmt_to_str(m_msg);
     static bool print_exc = MGB_GETENV("MGB_PRINT_EXC");
     if (print_exc) {
-        fprintf(stderr, "mgb: exception occurred: %s\n", msg.c_str());
+        fprintf(stderr, "mgb: exception occurred: %s\n", m_msg.c_str());
     }
 #endif
 }
diff --git a/src/core/include/megbrain/exception.h b/src/core/include/megbrain/exception.h
index 8af39ba90612aa709388d0dc53d5cd865ccaee3a..7c16e316e683454538b6db9c09e9cf5c753a3f31 100644
--- a/src/core/include/megbrain/exception.h
+++ b/src/core/include/megbrain/exception.h
@@ -90,7 +90,7 @@ class MegBrainError: public std::exception {
                 virtual ~ExtraInfo() = default;
         };
 
-        MegBrainError(const std::string &msg);
+        MegBrainError(const std::string& msg) : m_msg(msg) { init(); }
 
         const char *what() const noexcept override {
             return m_msg.c_str();
@@ -116,6 +116,7 @@ class MegBrainError: public std::exception {
 
     private:
         std::shared_ptr<ExtraInfo> m_extra_info;
+        void init();
 };
 
 //! base class for system error: error caused by uncontrollable environment
@@ -188,8 +189,14 @@ class TimeoutError final: public MegBrainError {
         using MegBrainError::MegBrainError;
 };
 
+
+}  // namespace mgb
+
+namespace mgb {
+
 bool has_uncaught_exception();
 
-} // namespace mgb
+}  // namespace mgb
+
 
 // vim: syntax=cpp.doxygen foldmethod=marker foldmarker=f{{{,f}}}