diff --git a/interface/src/avatar/FaceModel.cpp b/interface/src/avatar/FaceModel.cpp
index 6dd97f067a..722f998f86 100644
--- a/interface/src/avatar/FaceModel.cpp
+++ b/interface/src/avatar/FaceModel.cpp
@@ -87,6 +87,7 @@ void FaceModel::maybeUpdateEyeRotation(Model* model, const JointState& parentSta
 void FaceModel::updateJointState(int index) {
     JointState& state = _jointStates[index];
     const FBXJoint& joint = state.getFBXJoint();
+    // guard against out-of-bounds access to _jointStates
     if (joint.parentIndex != -1 && joint.parentIndex >= 0 && joint.parentIndex < _jointStates.size()) {
         const JointState& parentState = _jointStates.at(joint.parentIndex);
         const FBXGeometry& geometry = _geometry->getFBXGeometry();