diff --git a/doc/api/fs.md b/doc/api/fs.md
index 5cb4b9f422e9fb..881b17e684137e 100644
--- a/doc/api/fs.md
+++ b/doc/api/fs.md
@@ -1827,7 +1827,8 @@ added: v0.0.2
 
 Write `buffer` to the file specified by `fd`.
 
-`offset` and `length` determine the part of the buffer to be written.
+`offset` determines the part of the buffer to be written, and `length` is
+an integer specifying the number of bytes to write.
 
 `position` refers to the offset from the beginning of the file where this data
 should be written. If `typeof position !== 'number'`, the data will be written
@@ -2217,4 +2218,4 @@ The following constants are meant for use with the [`fs.Stats`][] object's
 [`event ports`]: http://illumos.org/man/port_create
 [`ReadDirectoryChangesW`]: https://msdn.microsoft.com/en-us/library/windows/desktop/aa365465%28v=vs.85%29.aspx
 [`AHAFS`]: https://www.ibm.com/developerworks/aix/library/au-aix_event_infrastructure/
-[Common System Errors]: errors.html#errors_common_system_errors
\ No newline at end of file
+[Common System Errors]: errors.html#errors_common_system_errors