add const
diff --git a/skeletons/per_decoder.h b/skeletons/per_decoder.h
index 0a50705..e97dd78 100644
--- a/skeletons/per_decoder.h
+++ b/skeletons/per_decoder.h
@@ -18,36 +18,37 @@
  * Unaligned PER decoder of a "complete encoding" as per X.691 (08/2015) #11.1.
  * On success, this call always returns (.consumed >= 1), as per #11.1.3.
  */
-asn_dec_rval_t uper_decode_complete(struct asn_codec_ctx_s *opt_codec_ctx,
-	struct asn_TYPE_descriptor_s *type_descriptor,	/* Type to decode */
-	void **struct_ptr,	/* Pointer to a target structure's pointer */
-	const void *buffer,	/* Data to be decoded */
-	size_t size		/* Size of data buffer */
-	);
+asn_dec_rval_t uper_decode_complete(
+    const struct asn_codec_ctx_s *opt_codec_ctx,
+    struct asn_TYPE_descriptor_s *type_descriptor, /* Type to decode */
+    void **struct_ptr,  /* Pointer to a target structure's pointer */
+    const void *buffer, /* Data to be decoded */
+    size_t size         /* Size of data buffer */
+    );
 
 /*
  * Unaligned PER decoder of any ASN.1 type. May be invoked by the application.
  * WARNING: This call returns the number of BITS read from the stream. Beware.
  */
-asn_dec_rval_t uper_decode(struct asn_codec_ctx_s *opt_codec_ctx,
-	struct asn_TYPE_descriptor_s *type_descriptor,	/* Type to decode */
-	void **struct_ptr,	/* Pointer to a target structure's pointer */
-	const void *buffer,	/* Data to be decoded */
-	size_t size,		/* Size of data buffer */
-	int skip_bits,		/* Number of unused leading bits, 0..7 */
-	int unused_bits		/* Number of unused tailing bits, 0..7 */
-	);
+asn_dec_rval_t uper_decode(
+    const struct asn_codec_ctx_s *opt_codec_ctx,
+    struct asn_TYPE_descriptor_s *type_descriptor, /* Type to decode */
+    void **struct_ptr,  /* Pointer to a target structure's pointer */
+    const void *buffer, /* Data to be decoded */
+    size_t size,        /* Size of data buffer */
+    int skip_bits,      /* Number of unused leading bits, 0..7 */
+    int unused_bits     /* Number of unused tailing bits, 0..7 */
+    );
 
 
 /*
  * Type of the type-specific PER decoder function.
  */
-typedef asn_dec_rval_t (per_type_decoder_f)(asn_codec_ctx_t *opt_codec_ctx,
-		struct asn_TYPE_descriptor_s *type_descriptor,
-		const asn_per_constraints_t *constraints,
-		void **struct_ptr,
-		asn_per_data_t *per_data
-	);
+typedef asn_dec_rval_t(per_type_decoder_f)(
+    const asn_codec_ctx_t *opt_codec_ctx,
+    struct asn_TYPE_descriptor_s *type_descriptor,
+    const asn_per_constraints_t *constraints, void **struct_ptr,
+    asn_per_data_t *per_data);
 
 #ifdef __cplusplus
 }