diff --git a/include/tinyalsa/pcm.h b/include/tinyalsa/pcm.h
index c2c67bb..caa4d1f 100644
--- a/include/tinyalsa/pcm.h
+++ b/include/tinyalsa/pcm.h
@@ -238,7 +238,7 @@ struct pcm *pcm_open(unsigned int card,
 
 int pcm_close(struct pcm *pcm);
 	
-int pcm_is_ready(struct pcm *pcm);
+int pcm_is_ready(const struct pcm *pcm);
 
 int pcm_get_file_descriptor(struct pcm *pcm);
 
diff --git a/src/pcm.c b/src/pcm.c
index 29c69a7..c32e8ab 100644
--- a/src/pcm.c
+++ b/src/pcm.c
@@ -979,7 +979,7 @@ fail_close:
  *  Otherwise, the function returns one.
  * @ingroup libtinyalsa-pcm
  */
-int pcm_is_ready(struct pcm *pcm)
+int pcm_is_ready(const struct pcm *pcm)
 {
     return pcm->fd >= 0;
 }