diff --git a/src/store.js b/src/store.js
index a79252b50..b32d7b0ad 100644
--- a/src/store.js
+++ b/src/store.js
@@ -301,6 +301,9 @@ function installModule (store, rootState, path, module, hot) {
 
   // register in namespace map
   if (module.namespaced) {
+    if (store._modulesNamespaceMap[namespace] && process.env.NODE_ENV !== 'production') {
+      console.error(`[vuex] duplicate namespace ${namespace} for the namespaced module ${path.join('/')}`)
+    }
     store._modulesNamespaceMap[namespace] = module
   }