diff --git a/src/constraint.c b/src/constraint.c
index d4f78dfa..7e5be6a1 100644
--- a/src/constraint.c
+++ b/src/constraint.c
@@ -26,7 +26,7 @@
   * \param state   encoder state
   * \return the pointer of constraint_t structure
   */
-void * kvz_init_constraint(encoder_state_t* state, encoder_control_t * encoder) {
+void * kvz_init_constraint(encoder_state_t* state, const encoder_control_t * const encoder) {
 	constraint_t* constr = NULL;
 	// Allocate the constraint_t strucutre
 	constr = MALLOC(constraint_t, 1);
diff --git a/src/constraint.h b/src/constraint.h
index 1af76834..53c81ddb 100644
--- a/src/constraint.h
+++ b/src/constraint.h
@@ -34,7 +34,7 @@ typedef struct {
 } constraint_t;
 
 
-void * kvz_init_constraint(encoder_state_t* state, encoder_control_t * encoder);
+void * kvz_init_constraint(encoder_state_t* state, const encoder_control_t * const);
 void kvz_constraint_free(encoder_state_t* state);
 
 #endif
\ No newline at end of file