diff --git a/src/common/remoteio.h b/src/common/remoteio.h
--- a/src/common/remoteio.h
+++ b/src/common/remoteio.h
@@ -38,7 +38,9 @@ int remoteio_open(struct remoteio **rem,
 
 /**
    non-blocking I/O.
-   @return 0 on success, 1 on failure
+   @param len must be greater than 0
+
+   @return 0 on success, 1 on failure. 
  */
 int remoteio_read(struct remoteio *rem, void *buf, size_t len, size_t *bytesread);
 int remoteio_write(struct remoteio *rem, void *buf, size_t len, size_t *byteswritten);