diff --git a/doc_src/doc.hdr b/doc_src/doc.hdr
index 17ff4e3e1..bdaebb48a 100644
--- a/doc_src/doc.hdr
+++ b/doc_src/doc.hdr
@@ -747,6 +747,10 @@ set -e smurf[1]
 echo $smurf
 </pre>
 
+If you specify a negative index when expanding or assigning to an
+array variable, the index will be calculated from the end of the
+array. For example, the index -1 means the last index of an array.
+
 \subsection variables-special Special variables
 
 The user can change the settings of \c fish by changing the values of
diff --git a/doc_src/set.txt b/doc_src/set.txt
index bc03c1e13..2a8b8d9f4 100644
--- a/doc_src/set.txt
+++ b/doc_src/set.txt
@@ -32,7 +32,12 @@ If the variable name is one or more array elements, such as
 <code>PATH[1 3 7]</code>, only those array elements specified will be
 changed. When array indices are specified to set, multiple arguments
 may be used to specify additional indexes, e.g. <code>set PATH[1]
-PATH[4] /bin /sbin</code>.
+PATH[4] /bin /sbin</code>. If you specify a negative index when
+expanding or assigning to an array variable, the index will be
+calculated from the end of the array. For example, the index -1 means
+the last index of an array.
+
+
 
 -# If a variable is explicitly set to either universal, global or local, that setting will be honored. If a variable of the same name exists in a different scope, that variable will not be changed.
 -# If a variable is not explicitly set to be either universal, global or local, but has been previously defined, the previos variable scope is used.