diff --git a/doc/api/fs.md b/doc/api/fs.md
index 4651e08672dda5..638e8261e36af1 100644
--- a/doc/api/fs.md
+++ b/doc/api/fs.md
@@ -1832,7 +1832,8 @@ 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