diff --git a/x/installing/libxcb.xml b/x/installing/libxcb.xml
index 1ec3553038..e41a25bf1f 100644
--- a/x/installing/libxcb.xml
+++ b/x/installing/libxcb.xml
@@ -104,7 +104,7 @@
       commands:
     </para>
 
-<screen><userinput>CFLAGS=-Wno-error=format-extra-args ./configure $XORG_CONFIG      \
+<screen><userinput>CFLAGS="${CFLAGS:--O2 -g} -Wno-error=format-extra-args" ./configure $XORG_CONFIG      \
             --without-doxygen \
             --docdir='${datadir}'/doc/libxcb-&libxcb-version; &amp;&amp;
 make</userinput></screen>