diff --git a/reference/datetime/datetime/createfromformat.xml b/reference/datetime/datetime/createfromformat.xml
index 11fb088db1..e46713cd04 100644
--- a/reference/datetime/datetime/createfromformat.xml
+++ b/reference/datetime/datetime/createfromformat.xml
@@ -86,7 +86,10 @@
          </row>
          <row>
           <entry><literal>z</literal></entry>
-          <entry>The day of the year (starting from 0)</entry>
+          <entry>
+           The day of the year (starting from 0);
+           must be preceeded by <literal>Y</literal> or <literal>y</literal>.
+          </entry>
           <entry><literal>0</literal> through <literal>365</literal></entry>
          </row>
          <row>