diff --git a/apps/mp3data.c b/apps/mp3data.c
index 4944e02f48..13ff0a87a7 100644
--- a/apps/mp3data.c
+++ b/apps/mp3data.c
@@ -379,8 +379,10 @@ static size_t mem_pos;
 static int mem_cnt;
 static int mem_maxlen;
 
-static int mem_getbyte(int /*dummy*/, unsigned char *c)
+static int mem_getbyte(int dummy, unsigned char *c)
 {
+    (void)dummy;
+
     *c = mem_buf[mem_pos++];
     if(mem_pos >= mem_buflen)
         mem_pos = 0;