diff --git a/manual/installation.rst b/manual/installation.rst
index 867c71d..bc4e0d2 100644
--- a/manual/installation.rst
+++ b/manual/installation.rst
@@ -659,7 +659,7 @@ Building with zopfli support
 
 .. cSpell:ignore DZOPFLI
 
-If you compile with ``-DZOPFLI-ON`` and have the `zopfli
+If you compile with ``-DZOPFLI=ON`` and have the `zopfli
 <https://github.com/google/zopfli>`__ development files available,
 qpdf will be built with zopfli support. See :ref:`zopfli` for
 information about using zopfli with qpdf.