diff --git a/procrunner/__init__.py b/procrunner/__init__.py
index 1a1e306..5babce6 100644
--- a/procrunner/__init__.py
+++ b/procrunner/__init__.py
@@ -400,7 +400,7 @@
     :param array command: Command line to be run, specified as array.
     :param timeout: Terminate program execution after this many seconds.
     :param boolean debug: Enable further debug messages.
-    :param stdin: Optional string that is passed to command stdin.
+    :param stdin: Optional bytestring that is passed to command stdin.
     :param boolean print_stdout: Pass stdout through to sys.stdout.
     :param boolean print_stderr: Pass stderr through to sys.stderr.
     :param callback_stdout: Optional function which is called for each