diff --git a/reference/math/functions/mt-getrandmax.xml b/reference/math/functions/mt-getrandmax.xml
index 1f82f810bc..2ae1b3c67a 100644
--- a/reference/math/functions/mt-getrandmax.xml
+++ b/reference/math/functions/mt-getrandmax.xml
@@ -19,7 +19,10 @@
  <refsect1 role="returnvalues">
   &reftitle.returnvalues;
   <para>
-   Returns the maximum random value returned by <function>mt_rand</function>
+   Returns the maximum random value returned by a call to
+   <function>mt_rand</function> without arguments, which is the maximum value 
+   that can be used for its <function>max</function> parameter without the
+   result being scaled up (and therefore less random).
   </para>
  </refsect1>
  <refsect1 role="examples">
diff --git a/reference/math/functions/mt-rand.xml b/reference/math/functions/mt-rand.xml
index 8e32a52c52..5643deb68d 100644
--- a/reference/math/functions/mt-rand.xml
+++ b/reference/math/functions/mt-rand.xml
@@ -124,6 +124,9 @@ echo mt_rand(5, 15);
     The distribution of <function>mt_rand</function> return values is biased
     towards even numbers on 64-bit builds of PHP when
     <parameter>max</parameter> is beyond <literal>2^32</literal>.
+    This is because if <parameter>max</parameter> is greater than 
+    the value returned by <function>mt_getrandmax</function>, the output of the
+    random number generator must be scaled up.
    </para>
   </caution>
  </refsect1>