diff --git a/src/xrt/auxiliary/util/u_hand_simulation.c b/src/xrt/auxiliary/util/u_hand_simulation.c
index 05211563a..4ec2f6dcb 100644
--- a/src/xrt/auxiliary/util/u_hand_simulation.c
+++ b/src/xrt/auxiliary/util/u_hand_simulation.c
@@ -390,9 +390,9 @@ u_hand_sim_simulate(struct u_hand_sim_hand *hand_ptr, struct xrt_hand_joint_set
 }
 
 void
-u_hand_sim_simulate_for_valve_index_knuckles(struct u_hand_tracking_curl_values *values,
+u_hand_sim_simulate_for_valve_index_knuckles(const struct u_hand_tracking_curl_values *values,
                                              bool is_right,
-                                             struct xrt_space_relation *root_pose,
+                                             const struct xrt_space_relation *root_pose,
                                              struct xrt_hand_joint_set *out_set)
 {
 	struct u_hand_sim_hand hand;
diff --git a/src/xrt/auxiliary/util/u_hand_simulation.h b/src/xrt/auxiliary/util/u_hand_simulation.h
index fb87b4be1..0a3d14569 100644
--- a/src/xrt/auxiliary/util/u_hand_simulation.h
+++ b/src/xrt/auxiliary/util/u_hand_simulation.h
@@ -70,9 +70,9 @@ void
 u_hand_sim_simulate(struct u_hand_sim_hand *hand, struct xrt_hand_joint_set *out_set);
 
 void
-u_hand_sim_simulate_for_valve_index_knuckles(struct u_hand_tracking_curl_values *values,
+u_hand_sim_simulate_for_valve_index_knuckles(const struct u_hand_tracking_curl_values *values,
                                              bool is_right,
-                                             struct xrt_space_relation *root_pose,
+                                             const struct xrt_space_relation *root_pose,
                                              struct xrt_hand_joint_set *out_set);
 
 void