diff --git a/include/opus_multistream.h b/include/opus_multistream.h
index e6562a7..5e5364a 100644
--- a/include/opus_multistream.h
+++ b/include/opus_multistream.h
@@ -54,7 +54,7 @@
 /** Allocate and initialize a multistream encoder state object.
  *  Call opus_multistream_encoder_destroy() to release
  *  this object when finished. */
-OPUS_EXPORT OpusMSEncoder *opus_multistream_encoder_create(
+OPUS_EXPORT OPUS_WARN_UNUSED_RESULT OpusMSEncoder *opus_multistream_encoder_create(
       opus_int32 Fs,            /**< Sampling rate of input signal (Hz) */
       int channels,             /**< Number of channels in the input signal */
       int streams,              /**< Total number of streams to encode from the input */
@@ -62,7 +62,7 @@
       const unsigned char *mapping, /**< Encoded mapping between channels and streams */
       int application,          /**< Coding mode (OPUS_APPLICATION_VOIP/OPUS_APPLICATION_AUDIO) */
       int *error                /**< Error code */
-);
+) OPUS_ARG_NONNULL(5);
 
 /** Initialize an already allocated multistream encoder state. */
 OPUS_EXPORT int opus_multistream_encoder_init(
@@ -73,30 +73,30 @@
       int coupled_streams,      /**< Number of coupled (stereo) streams to encode */
       const unsigned char *mapping, /**< Encoded mapping between channels and streams */
       int application           /**< Coding mode (OPUS_APPLICATION_VOIP/OPUS_APPLICATION_AUDIO) */
-);
+) OPUS_ARG_NONNULL(1) OPUS_ARG_NONNULL(6);
 
 /** Returns length of the data payload (in bytes) or a negative error code */
-OPUS_EXPORT int opus_multistream_encode(
+OPUS_EXPORT OPUS_WARN_UNUSED_RESULT int opus_multistream_encode(
     OpusMSEncoder *st,          /**< Encoder state */
     const opus_int16 *pcm,      /**< Input signal as interleaved samples. Length is frame_size*channels */
     int frame_size,             /**< Number of samples per frame of input signal */
     unsigned char *data,        /**< Output buffer for the compressed payload (no more than max_data_bytes long) */
     opus_int32 max_data_bytes   /**< Allocated memory for payload; don't use for controlling bitrate */
-);
+) OPUS_ARG_NONNULL(1) OPUS_ARG_NONNULL(2) OPUS_ARG_NONNULL(4);
 
 /** Returns length of the data payload (in bytes) or a negative error code. */
-OPUS_EXPORT int opus_multistream_encode_float(
+OPUS_EXPORT OPUS_WARN_UNUSED_RESULT int opus_multistream_encode_float(
       OpusMSEncoder *st,        /**< Encoder state */
       const float *pcm,         /**< Input signal interleaved in channel order. length is frame_size*channels */
       int frame_size,           /**< Number of samples per frame of input signal */
       unsigned char *data,      /**< Output buffer for the compressed payload (no more than max_data_bytes long) */
       opus_int32 max_data_bytes /**< Allocated memory for payload; don't use for controlling bitrate */
-  );
+) OPUS_ARG_NONNULL(1) OPUS_ARG_NONNULL(2) OPUS_ARG_NONNULL(4);
 
 /** Gets the size of an OpusMSEncoder structure.
   * @returns size
   */
-OPUS_EXPORT opus_int32 opus_multistream_encoder_get_size(
+OPUS_EXPORT OPUS_WARN_UNUSED_RESULT opus_int32 opus_multistream_encoder_get_size(
       int streams,              /**< Total number of coded streams */
       int coupled_streams       /**< Number of coupled (stereo) streams */
 );
@@ -105,19 +105,19 @@
 OPUS_EXPORT void opus_multistream_encoder_destroy(OpusMSEncoder *st);
 
 /** Get or set options on a multistream encoder state */
-OPUS_EXPORT int opus_multistream_encoder_ctl(OpusMSEncoder *st, int request, ...);
+OPUS_EXPORT int opus_multistream_encoder_ctl(OpusMSEncoder *st, int request, ...) OPUS_ARG_NONNULL(1);
 
 /** Allocate and initialize a multistream decoder state object.
  *  Call opus_multistream_decoder_destroy() to release
  *  this object when finished. */
-OPUS_EXPORT OpusMSDecoder *opus_multistream_decoder_create(
+OPUS_EXPORT OPUS_WARN_UNUSED_RESULT OpusMSDecoder *opus_multistream_decoder_create(
       opus_int32 Fs,            /**< Sampling rate to decode at (Hz) */
       int channels,             /**< Number of channels to decode */
       int streams,              /**< Total number of coded streams in the multistream */
       int coupled_streams,      /**< Number of coupled (stereo) streams in the multistream */
       const unsigned char *mapping, /**< Stream to channel mapping table */
       int *error                /**< Error code */
-);
+) OPUS_ARG_NONNULL(5);
 
 /** Intialize a previously allocated decoder state object. */
 OPUS_EXPORT int opus_multistream_decoder_init(
@@ -127,10 +127,10 @@
       int streams,              /**< Total number of coded streams */
       int coupled_streams,      /**< Number of coupled (stereo) streams */
       const unsigned char *mapping  /**< Stream to channel mapping table */
-);
+) OPUS_ARG_NONNULL(1) OPUS_ARG_NONNULL(6);
 
 /** Returns the number of samples decoded or a negative error code */
-OPUS_EXPORT int opus_multistream_decode(
+OPUS_EXPORT OPUS_WARN_UNUSED_RESULT int opus_multistream_decode(
     OpusMSDecoder *st,          /**< Decoder state */
     const unsigned char *data,  /**< Input payload. Use a NULL pointer to indicate packet loss */
     opus_int32 len,             /**< Number of bytes in payload */
@@ -138,10 +138,10 @@
     int frame_size,             /**< Number of samples per frame of input signal */
     int decode_fec              /**< Flag (0/1) to request that any in-band forward error correction data be */
                                 /**< decoded. If no such data is available the frame is decoded as if it were lost. */
-);
+) OPUS_ARG_NONNULL(1) OPUS_ARG_NONNULL(4);
 
 /** Returns the number of samples decoded or a negative error code */
-OPUS_EXPORT int opus_multistream_decode_float(
+OPUS_EXPORT OPUS_WARN_UNUSED_RESULT int opus_multistream_decode_float(
     OpusMSDecoder *st,          /**< Decoder state */
     const unsigned char *data,  /**< Input payload buffer. Use a NULL pointer to indicate packet loss */
     opus_int32 len,             /**< Number of payload bytes in data */
@@ -149,18 +149,18 @@
     int frame_size,             /**< Number of samples per frame of input signal */
     int decode_fec              /**< Flag (0/1) to request that any in-band forward error correction data be */
                                 /**< decoded. If no such data is available the frame is decoded as if it were lost. */
-);
+) OPUS_ARG_NONNULL(1) OPUS_ARG_NONNULL(4);
 
 /** Gets the size of an OpusMSDecoder structure.
   * @returns size
   */
-OPUS_EXPORT opus_int32 opus_multistream_decoder_get_size(
+OPUS_EXPORT OPUS_WARN_UNUSED_RESULT opus_int32 opus_multistream_decoder_get_size(
       int streams,              /**< Total number of coded streams */
       int coupled_streams       /**< Number of coupled (stereo) streams */
 );
 
 /** Get or set options on a multistream decoder state */
-OPUS_EXPORT int opus_multistream_decoder_ctl(OpusMSDecoder *st, int request, ...);
+OPUS_EXPORT int opus_multistream_decoder_ctl(OpusMSDecoder *st, int request, ...) OPUS_ARG_NONNULL(1);
 
 /** Deallocate a multistream decoder state object */
 OPUS_EXPORT void opus_multistream_decoder_destroy(OpusMSDecoder *st);