document -a
diff --git a/man/man1/diff.1 b/man/man1/diff.1
index dbb598e..fd42643 100644
--- a/man/man1/diff.1
+++ b/man/man1/diff.1
@@ -4,7 +4,7 @@
 .SH SYNOPSIS
 .B diff
 [
-.B -cefmnbwr
+.B -acefmnbwr
 ] file1 ... file2
 .SH DESCRIPTION
 .I Diff
@@ -127,6 +127,9 @@
 .B -c
 option includes three lines of context around each
 change, merging changes whose contexts overlap.
+The
+.B -a
+flag displays the entire file as context.
 .PP
 Except in rare circumstances,
 .I diff