diff --git a/language/namespaces.xml b/language/namespaces.xml
index 64090d3836..58c65ed608 100644
--- a/language/namespaces.xml
+++ b/language/namespaces.xml
@@ -130,6 +130,12 @@ function connect() { /* ... */ }
 ]]>
     </programlisting>
    </example>
+   <note>
+    <simpara>
+     Fully qualified names (i.e. names starting with a backslash) are not allowed in namespace
+     declarations, because such constructs are interpreted as relative namespace expressions.
+    </simpara>
+   </note>
    The only code construct allowed before a namespace declaration is the
    <literal>declare</literal> statement, for defining encoding of a source file.  In addition,
    no non-PHP code may precede a namespace declaration, including extra whitespace: