diff --git a/libstdc++-v3/doc/html/faq.html b/libstdc++-v3/doc/html/faq.html
index 967e5f5f348..f49b84c4c33 100644
--- a/libstdc++-v3/doc/html/faq.html
+++ b/libstdc++-v3/doc/html/faq.html
@@ -456,7 +456,7 @@
          <code class="varname">CPLUSPLUS_CPP_SPEC</code> in
          the gcc config headers for your target (and try changing them to
          see what happens when building complicated code).  You can also run
-         <span class="command"><strong>g++ -E -dM - &lt; /dev/null"</strong></span> to display
+         <span class="command"><strong>g++ -E -dM -x c++ /dev/null</strong></span> to display
          a list of predefined macros for any particular installation.
       </p><p>This has been discussed on the mailing lists
          <a class="link" href="http://gcc.gnu.org/cgi-bin/htsearch?method=and&amp;format=builtin-long&amp;sort=score&amp;words=_XOPEN_SOURCE+Solaris" target="_top">quite a bit</a>.
diff --git a/libstdc++-v3/doc/xml/faq.xml b/libstdc++-v3/doc/xml/faq.xml
index e419d3c22a0..9ae4966ecea 100644
--- a/libstdc++-v3/doc/xml/faq.xml
+++ b/libstdc++-v3/doc/xml/faq.xml
@@ -580,7 +580,7 @@
          <varname>CPLUSPLUS_CPP_SPEC</varname> in
          the gcc config headers for your target (and try changing them to
          see what happens when building complicated code).  You can also run
-         <command>g++ -E -dM - &lt; /dev/null"</command> to display
+         <command>g++ -E -dM -x c++ /dev/null</command> to display
          a list of predefined macros for any particular installation.
       </para>
       <para>This has been discussed on the mailing lists