diff --git a/libisoburn/trunk/README b/libisoburn/trunk/README
index 891b626a..0c44d3ff 100644
--- a/libisoburn/trunk/README
+++ b/libisoburn/trunk/README
@@ -83,11 +83,11 @@ Never omit the "make clean" command after switching libreadline enabling.
 Other deliberate dependency reduction options of ./configure are:
     --disable-libacl   avoid use of ACL functions like acl_to_text()
     --disable-xattr    avoid use of xattr functions like listxattr()
+    --disable-zlib     avoid use of zlib functions like compress2()
 
 xorriso allows to use external processes as file content filters. This is
 a potential security risk which may be avoided by ./configure option
     --disable-external-filters
-
 By default the filter feature is disabled if effective user id and real
 user id differ. This ban can be lifted by
     --enable-external-filters-setuid
diff --git a/libisoburn/trunk/xorriso/README b/libisoburn/trunk/xorriso/README
index 32bef826..fb196764 100644
--- a/libisoburn/trunk/xorriso/README
+++ b/libisoburn/trunk/xorriso/README
@@ -42,6 +42,7 @@ components:
 Optional at compile time are:
    libreadline and the readline-dev headers make dialog mode more convenient.
    on Linux: libacl and libacl-devel allow getting and setting ACLs.
+   zlib and zlib-devel allow zisofs compression.
 If they were present at compile time, then the optional libraries have to
 be present at runtime, too.
 
@@ -91,6 +92,7 @@ Never omit the "make clean" command after switching libreadline enabling.
 Other deliberate dependency reduction options of ./configure are:
     --disable-libacl   avoid use of ACL functions like acl_to_text()
     --disable-xattr    avoid use of xattr functions like listxattr()
+    --disable-zlib     avoid use of zlib functions like compress2()
 
 xorriso allows to use external processes as file content filters. This is
 a potential security risk which may be avoided by ./configure option