diff --git a/src/user/user_objects.cc b/src/user/user_objects.cc
index 3e4c61bf..9654182c 100644
--- a/src/user/user_objects.cc
+++ b/src/user/user_objects.cc
@@ -873,10 +873,6 @@ mjCBody& mjCBody::operator+=(const mjCFrame& other) {
   other.model->suffix = other.suffix;
   other.model->StoreKeyframes(model);
 
-  if (other.prefix.empty() && other.suffix.empty()) {
-    throw mjCError(this, "either prefix or suffix must be non-empty");
-  }
-
   // attach defaults
   if (other.model != model) {
     mjCDef* subdef = new mjCDef(*other.model->Default());
@@ -1845,10 +1841,6 @@ mjCFrame& mjCFrame::operator+=(const mjCBody& other) {
   other.model->prefix = "";
   other.model->suffix = "";
 
-  if (other.prefix.empty() && other.suffix.empty()) {
-    throw mjCError(this, "either prefix or suffix must be non-empty");
-  }
-
   mjCBody* subtree = new mjCBody(other, model);
   other.ForgetKeyframes();
   other.model->prefix = subtree->prefix;