diff --git a/src/gsm/gsm48.c b/src/gsm/gsm48.c
index 17b0829..43b10b7 100644
--- a/src/gsm/gsm48.c
+++ b/src/gsm/gsm48.c
@@ -737,10 +737,12 @@
  *  \param[in] str_len Length of \a string in bytes
  *  \param[in] mi Mobile Identity to be stringified
  *  \param[in] mi_len Length of \a mi in bytes
- *  \returns WARNING: the return value of this function is not well implemented.
+ *  \returns Return <= 0 on error, > 0 on success.
+ *           WARNING: the return value of this function is not well implemented.
  *           Depending on the MI type and amount of output buffer, this may return
  *           the nr of written bytes, or the written strlen(), or the snprintf()
- *           style strlen()-if-the-buffer-were-large-enough. */
+ *           style strlen()-if-the-buffer-were-large-enough.
+ */
 int gsm48_mi_to_string(char *string, int str_len, const uint8_t *mi, int mi_len)
 {
 	int rc;