diff --git a/auth/cas/CAS/CAS.php b/auth/cas/CAS/CAS.php
index 38c4cf672d241..52fe40178ab3d 100644
--- a/auth/cas/CAS/CAS.php
+++ b/auth/cas/CAS/CAS.php
@@ -32,7 +32,7 @@
 //
 // hack by Vangelis Haniotakis to handle the absence of $_SERVER['REQUEST_URI'] in IIS
 //
-if (!$_SERVER['REQUEST_URI']) {
+if (!isset($_SERVER['REQUEST_URI'])) {
 	$_SERVER['REQUEST_URI'] = $_SERVER['SCRIPT_NAME'] . '?' . $_SERVER['QUERY_STRING'];
 }
 
diff --git a/auth/cas/CAS/readme_moodle.txt b/auth/cas/CAS/readme_moodle.txt
new file mode 100644
index 0000000000000..91a4956ccfc63
--- /dev/null
+++ b/auth/cas/CAS/readme_moodle.txt
@@ -0,0 +1,8 @@
+Description of phpCAS 1.1.2 library import into Moodle
+
+Our changes:
+ * CAS.php - fix notice of $_SERVER['REQUEST_URI'] not being defined under IIS
+   (we can remove this change when we upgrade to a phpCAS version that has
+    https://issues.jasig.org/browse/PHPCAS-81 fixed).
+
+iarenaza