diff --git a/skeletons/oer_encoder.h b/skeletons/oer_encoder.h
index 6d33f1c..03ddfce 100644
--- a/skeletons/oer_encoder.h
+++ b/skeletons/oer_encoder.h
@@ -26,7 +26,7 @@
 /* A variant of oer_encode() which encodes data into the pre-allocated buffer */
 asn_enc_rval_t oer_encode_to_buffer(
     struct asn_TYPE_descriptor_s *type_descriptor,
-    asn_oer_constraints_t *constraints,
+    const asn_oer_constraints_t *constraints,
     void *struct_ptr,  /* Structure to be encoded */
     void *buffer,      /* Pre-allocated buffer */
     size_t buffer_size /* Initial buffer size (maximum) */
@@ -37,7 +37,7 @@
  */
 typedef asn_enc_rval_t(oer_type_encoder_f)(
     struct asn_TYPE_descriptor_s *type_descriptor,
-    asn_oer_constraints_t *constraints,
+    const asn_oer_constraints_t *constraints,
     void *struct_ptr,                          /* Structure to be encoded */
     asn_app_consume_bytes_f *consume_bytes_cb, /* Callback */
     void *app_key                              /* Arbitrary callback argument */