diff --git a/MANUAL.txt b/MANUAL.txt
index 8c6dba9d..c77410aa 100644
--- a/MANUAL.txt
+++ b/MANUAL.txt
@@ -168,6 +168,12 @@ Options:
           Use the much slower but stronger Zopfli compressor for main compression trials.
           Recommended use is with '-o max' and '--fast'.
 
+      --zi <iterations>
+          Set the number of iterations to use for Zopfli compression. Using fewer iterations may
+          speed up compression for large files. This option requires '--zopfli' to be set.
+          
+          [default: 15]
+
       --timeout <secs>
           Maximum amount of time, in seconds, to spend on optimizations. Oxipng will check the
           timeout before each transformation or compression trial, and will stop trying to optimize