diff --git a/icu4c/readme.html b/icu4c/readme.html
index 806fbe447e..1cd9dff932 100644
--- a/icu4c/readme.html
+++ b/icu4c/readme.html
@@ -87,6 +87,8 @@
 
           <li><a href="#ImportantNotesUnix">Unix Type Platforms</a></li>
 
+          <li><a href="#ImportantNotesDefaultCP">Using the default codepage</a></li>
+
           <li><a href="#ImportantNotesDeprecatedAPI">Methods for enabling
           deprecated APIs</a></li>
         </ul>
@@ -1412,6 +1414,17 @@ ADDENVVAR ENVVAR(OUTPUTDIR) VALUE('<i>libraryname</i>')</samp>
     LD_LIBRARY_PATH environment variable. The ICU libraries may not link or
     load properly without doing this.</p>
 
+    <h3><a name="ImportantNotesDefaultCP">Using the default codepage</a></h3>
+
+    <p>Starting in ICU 2.0, when the default codepage cannot be opened, a
+    fallback default codepage will be used.  On most platforms, this will be
+    US-ASCII. For os/390 (z/OS), ibm-1047-s390 is the default fallback
+    codepage. For as/400 (iSeries), ibm-37 is the default fallback codepage.
+    This default fallback codepage is used when the operating system is using
+    a non-standard name for a default codepage, or the converter was not
+    packaged with ICU. The feature allows ICU to run in unusual
+    computing environments without completely failing.</p>
+
     <h3><a name="ImportantNotesDeprecatedAPI">Methods for enabling deprecated
     APIs</a></h3>