diff --git a/language/types/float.xml b/language/types/float.xml
index 3fd2946641..e64debed11 100644
--- a/language/types/float.xml
+++ b/language/types/float.xml
@@ -88,6 +88,22 @@ EXPONENT_DNUM [+-]?(({LNUM} | {DNUM}) [eE][+-]? {LNUM})
   </para>
 
  </sect2>
+ 
+ <sect2 xml:id="language.types.float.nan">
+  <title>NaN</title>
+  <para>
+   Some numeric operations can result in a value represented by the constant
+   <constant>NAN</constant>. This result represents an undefined or
+   unrepresentable value in floating-point calculations. Any loose or strict
+   comparisons of this value against any other value, including itself, will
+   have a result of &false;.
+  </para>
+  <para>
+   Because <constant>NAN</constant> represents any number of different values,
+   <constant>NAN</constant> should not be compared to other values, including
+   itself, and instead should be checked for using <function>is_nan</function>.
+  </para>
+ </sect2>
 </sect1>
 
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