diff --git a/reference/datetime/functions/strftime.xml b/reference/datetime/functions/strftime.xml
index 026bc8858c..1a7a2b706f 100644
--- a/reference/datetime/functions/strftime.xml
+++ b/reference/datetime/functions/strftime.xml
@@ -332,6 +332,14 @@
  <refsect1 role="errors">
   &reftitle.errors;
   &date.timezone.errors.description;
+  <para>
+   As the output is dependent upon the underlying C library, some conversion
+   specifiers are not supported. On Windows, supplying unknown conversion
+   specifiers will result in 5 <constant>E_WARNING</constant> messages and
+   return &false;. On other operating systems you may not get any
+   <constant>E_WARNING</constant> messages and the output may contain the
+   conversion specifiers unconverted.
+  </para>
  </refsect1>
 
  <refsect1 role="changelog">