diff --git a/part3intro/generalinstructions.xml b/part3intro/generalinstructions.xml
index 0739f79cc..d8e280e0d 100644
--- a/part3intro/generalinstructions.xml
+++ b/part3intro/generalinstructions.xml
@@ -97,6 +97,12 @@
               to be built.  In <xref linkend="chapter-cross-tools"/> and
               <xref linkend="chapter-temporary-tools"/>, ensure you are
               the <emphasis>lfs</emphasis> user when extracting the package.</para>
+              <para>All methods to get the source code tree being built
+              in-position, except extracting the package tarball, are not
+              supported. Notably, using <command>cp -R</command> to copy the
+              source code tree somewhere else can destroy links and
+              timestamps in the sources tree and cause building
+              failure.</para>
             </listitem>
             <listitem>
               <para>Change to the directory created when the package was