diff --git a/doc/funcref b/doc/funcref
index 545a068..612bcc9 100644
--- a/doc/funcref
+++ b/doc/funcref
@@ -850,4 +850,6 @@ Description:
  If file_path is NULL, then comedilib will use its the default
  file location.  The calibration information used by this function
  is generated by the comedi_calibrate program (see its man page).
+Returns:
+ Zero on success, a negative number on failure.