diff --git a/README.md b/README.md
index e105f9e..7baf54e 100644
--- a/README.md
+++ b/README.md
@@ -119,7 +119,9 @@ Both methods should block until either:
 - `count` bytes of data are read/written
 - the byte timeout, with `byte_timeout_ms >= 0`, expires
 
-A value `< 0` for `byte_timeout_ms` means no timeout.
+A value `< 0` for `byte_timeout_ms` means infinite timeout.  
+With a value `== 0` for `byte_timeout_ms`, the method should read/write once in a non-blocking fashion and return
+immediately.
 
 Their return value should be the number of bytes actually read/written, or `< 0` in case of error.  
 A return value between `0` and `count - 1` will be treated as if a timeout occurred on the transport side. All other
diff --git a/nanomodbus.h b/nanomodbus.h
index f2d1bc6..5cc814c 100644
--- a/nanomodbus.h
+++ b/nanomodbus.h
@@ -134,7 +134,9 @@ typedef enum nmbs_transport {
  * - `count` bytes of data are read/written
  * - the byte timeout, with `byte_timeout_ms >= 0`, expires
  *
- * A value `< 0` for `byte_timeout_ms` means no timeout.
+ * A value `< 0` for `byte_timeout_ms` means infinite timeout.
+ * With a value `== 0` for `byte_timeout_ms`, the method should read/write once in a non-blocking fashion and return immediately.
+ *
  *
  * Their return value should be the number of bytes actually read/written, or `< 0` in case of error.
  * A return value between `0` and `count - 1` will be treated as if a timeout occurred on the transport side. All other