diff --git a/pkg/apigateway/handler/request.go b/pkg/apigateway/handler/request.go
index 13a3ece3be..f910960622 100644
--- a/pkg/apigateway/handler/request.go
+++ b/pkg/apigateway/handler/request.go
@@ -143,7 +143,9 @@ func (req Request) findMod(resKey string) (modulebase.Manager, error) {
 	resName := req.params[resKey]
 	module, err := modulebase.GetModule(req.session, resName)
 	if err != nil {
-		return nil, errors.Errorf("found module by %s: %v", resName, err)
+		// preserve the error chain, so unknown modules (cause
+		// errors.ErrNotFound) are reported as 404 instead of 500
+		return nil, errors.Wrapf(err, "found module by %s", resName)
 	}
 	if module == nil {
 		return nil, httperrors.NewNotFoundError("resource %s module not exists", resName)
diff --git a/pkg/mcclient/modulebase/modules.go b/pkg/mcclient/modulebase/modules.go
index 2e72018c51..94772cd4d2 100644
--- a/pkg/mcclient/modulebase/modules.go
+++ b/pkg/mcclient/modulebase/modules.go
@@ -294,7 +294,9 @@ func registerAllJointModules() {
 func _getModule(session *mcclient.ClientSession, name string) (IBaseManager, error) {
 	mods, ok := modules[name]
 	if !ok {
-		return nil, fmt.Errorf("No such module %s", name)
+		// unknown module means the request URL does not exist: a client
+		// error (404), not a server error
+		return nil, errors.Wrapf(errors.ErrNotFound, "No such module %s", name)
 	}
 
 	if len(mods) == 1 {