diff --git a/admin/environment.xml b/admin/environment.xml
index 0afa5ecc001..61af243bbff 100644
--- a/admin/environment.xml
+++ b/admin/environment.xml
@@ -227,7 +227,7 @@
     <PHP_EXTENSIONS>
       <PHP_EXTENSION name="iconv" level="required">
         <FEEDBACK>
-          <ON_CHECK message="iconvrequired" />
+          <ON_ERROR message="iconvrequired" />
         </FEEDBACK>
       </PHP_EXTENSION>
       <PHP_EXTENSION name="mbstring" level="optional">
@@ -237,7 +237,7 @@
       </PHP_EXTENSION>
       <PHP_EXTENSION name="curl" level="required">
         <FEEDBACK>
-          <ON_CHECK message="curlrequired" />
+          <ON_ERROR message="curlrequired" />
         </FEEDBACK>
       </PHP_EXTENSION>
       <PHP_EXTENSION name="openssl" level="optional">
@@ -277,12 +277,12 @@
       </PHP_EXTENSION>
       <PHP_EXTENSION name="simplexml" level="required">
         <FEEDBACK>
-          <ON_CHECK message="simplexmlrequired" />
+          <ON_ERROR message="simplexmlrequired" />
         </FEEDBACK>
       </PHP_EXTENSION>
       <PHP_EXTENSION name="spl" level="required">
         <FEEDBACK>
-          <ON_CHECK message="splrequired" />
+          <ON_ERROR message="splrequired" />
         </FEEDBACK>
       </PHP_EXTENSION>
       <PHP_EXTENSION name="pcre" level="required">
@@ -344,7 +344,7 @@
     <PHP_EXTENSIONS>
       <PHP_EXTENSION name="iconv" level="required">
         <FEEDBACK>
-          <ON_CHECK message="iconvrequired" />
+          <ON_ERROR message="iconvrequired" />
         </FEEDBACK>
       </PHP_EXTENSION>
       <PHP_EXTENSION name="mbstring" level="optional">
@@ -354,7 +354,7 @@
       </PHP_EXTENSION>
       <PHP_EXTENSION name="curl" level="required">
         <FEEDBACK>
-          <ON_CHECK message="curlrequired" />
+          <ON_ERROR message="curlrequired" />
         </FEEDBACK>
       </PHP_EXTENSION>
       <PHP_EXTENSION name="openssl" level="optional">
@@ -394,12 +394,12 @@
       </PHP_EXTENSION>
       <PHP_EXTENSION name="simplexml" level="required">
         <FEEDBACK>
-          <ON_CHECK message="simplexmlrequired" />
+          <ON_ERROR message="simplexmlrequired" />
         </FEEDBACK>
       </PHP_EXTENSION>
       <PHP_EXTENSION name="spl" level="required">
         <FEEDBACK>
-          <ON_CHECK message="splrequired" />
+          <ON_ERROR message="splrequired" />
         </FEEDBACK>
       </PHP_EXTENSION>
       <PHP_EXTENSION name="pcre" level="required">
@@ -454,7 +454,7 @@
     <PHP_EXTENSIONS>
       <PHP_EXTENSION name="iconv" level="required">
         <FEEDBACK>
-          <ON_CHECK message="iconvrequired" />
+          <ON_ERROR message="iconvrequired" />
         </FEEDBACK>
       </PHP_EXTENSION>
       <PHP_EXTENSION name="mbstring" level="optional">
@@ -464,7 +464,7 @@
       </PHP_EXTENSION>
       <PHP_EXTENSION name="curl" level="required">
         <FEEDBACK>
-          <ON_CHECK message="curlrequired" />
+          <ON_ERROR message="curlrequired" />
         </FEEDBACK>
       </PHP_EXTENSION>
       <PHP_EXTENSION name="openssl" level="optional">
@@ -504,12 +504,12 @@
       </PHP_EXTENSION>
       <PHP_EXTENSION name="simplexml" level="required">
         <FEEDBACK>
-          <ON_CHECK message="simplexmlrequired" />
+          <ON_ERROR message="simplexmlrequired" />
         </FEEDBACK>
       </PHP_EXTENSION>
       <PHP_EXTENSION name="spl" level="required">
         <FEEDBACK>
-          <ON_CHECK message="splrequired" />
+          <ON_ERROR message="splrequired" />
         </FEEDBACK>
       </PHP_EXTENSION>
       <PHP_EXTENSION name="pcre" level="required">
@@ -569,7 +569,7 @@
     <PHP_EXTENSIONS>
       <PHP_EXTENSION name="iconv" level="required">
         <FEEDBACK>
-          <ON_CHECK message="iconvrequired" />
+          <ON_ERROR message="iconvrequired" />
         </FEEDBACK>
       </PHP_EXTENSION>
       <PHP_EXTENSION name="mbstring" level="optional">
@@ -579,7 +579,7 @@
       </PHP_EXTENSION>
       <PHP_EXTENSION name="curl" level="required">
         <FEEDBACK>
-          <ON_CHECK message="curlrequired" />
+          <ON_ERROR message="curlrequired" />
         </FEEDBACK>
       </PHP_EXTENSION>
       <PHP_EXTENSION name="openssl" level="optional">
@@ -619,12 +619,12 @@
       </PHP_EXTENSION>
       <PHP_EXTENSION name="simplexml" level="required">
         <FEEDBACK>
-          <ON_CHECK message="simplexmlrequired" />
+          <ON_ERROR message="simplexmlrequired" />
         </FEEDBACK>
       </PHP_EXTENSION>
       <PHP_EXTENSION name="spl" level="required">
         <FEEDBACK>
-          <ON_CHECK message="splrequired" />
+          <ON_ERROR message="splrequired" />
         </FEEDBACK>
       </PHP_EXTENSION>
       <PHP_EXTENSION name="pcre" level="required">
@@ -685,7 +685,7 @@
     <PHP_EXTENSIONS>
       <PHP_EXTENSION name="iconv" level="required">
         <FEEDBACK>
-          <ON_CHECK message="iconvrequired" />
+          <ON_ERROR message="iconvrequired" />
         </FEEDBACK>
       </PHP_EXTENSION>
       <PHP_EXTENSION name="mbstring" level="optional">
@@ -695,7 +695,7 @@
       </PHP_EXTENSION>
       <PHP_EXTENSION name="curl" level="required">
         <FEEDBACK>
-          <ON_CHECK message="curlrequired" />
+          <ON_ERROR message="curlrequired" />
         </FEEDBACK>
       </PHP_EXTENSION>
       <PHP_EXTENSION name="openssl" level="optional">
@@ -735,12 +735,12 @@
       </PHP_EXTENSION>
       <PHP_EXTENSION name="simplexml" level="required">
         <FEEDBACK>
-          <ON_CHECK message="simplexmlrequired" />
+          <ON_ERROR message="simplexmlrequired" />
         </FEEDBACK>
       </PHP_EXTENSION>
       <PHP_EXTENSION name="spl" level="required">
         <FEEDBACK>
-          <ON_CHECK message="splrequired" />
+          <ON_ERROR message="splrequired" />
         </FEEDBACK>
       </PHP_EXTENSION>
       <PHP_EXTENSION name="pcre" level="required">
@@ -801,7 +801,7 @@
     <PHP_EXTENSIONS>
       <PHP_EXTENSION name="iconv" level="required">
         <FEEDBACK>
-          <ON_CHECK message="iconvrequired" />
+          <ON_ERROR message="iconvrequired" />
         </FEEDBACK>
       </PHP_EXTENSION>
       <PHP_EXTENSION name="mbstring" level="optional">
@@ -811,7 +811,7 @@
       </PHP_EXTENSION>
       <PHP_EXTENSION name="curl" level="required">
         <FEEDBACK>
-          <ON_CHECK message="curlrequired" />
+          <ON_ERROR message="curlrequired" />
         </FEEDBACK>
       </PHP_EXTENSION>
       <PHP_EXTENSION name="openssl" level="optional">
@@ -851,12 +851,12 @@
       </PHP_EXTENSION>
       <PHP_EXTENSION name="simplexml" level="required">
         <FEEDBACK>
-          <ON_CHECK message="simplexmlrequired" />
+          <ON_ERROR message="simplexmlrequired" />
         </FEEDBACK>
       </PHP_EXTENSION>
       <PHP_EXTENSION name="spl" level="required">
         <FEEDBACK>
-          <ON_CHECK message="splrequired" />
+          <ON_ERROR message="splrequired" />
         </FEEDBACK>
       </PHP_EXTENSION>
       <PHP_EXTENSION name="pcre" level="required">
diff --git a/lib/environmentlib.php b/lib/environmentlib.php
index be7aabf68a7..3d8a0dffd33 100644
--- a/lib/environmentlib.php
+++ b/lib/environmentlib.php
@@ -70,6 +70,10 @@ defined('MOODLE_INTERNAL') || die();
     define('CUSTOM_CHECK_FUNCTION_MISSING',     14);
     /** XML Processing Error */
     define('NO_PHP_SETTINGS_NAME_FOUND',        15);
+    /** XML Processing Error */
+    define('INCORRECT_FEEDBACK_FOR_REQUIRED',   16);
+    /** XML Processing Error */
+    define('INCORRECT_FEEDBACK_FOR_OPTIONAL',   17);
 
 /// Define algorithm used to select the xml file
     /** To select the newer file available to perform checks */
@@ -1066,6 +1070,8 @@ function process_environment_restrict($xml, &$result) {
  * This function will detect if there is some message available to be added to the
  * result in order to clarify enviromental details.
  *
+ * @uses INCORRECT_FEEDBACK_FOR_REQUIRED
+ * @uses INCORRECT_FEEDBACK_FOR_OPTIONAL
  * @param string xmldata containing the feedback data
  * @param object reult object to be updated
  */
@@ -1075,6 +1081,15 @@ function process_environment_messages($xml, &$result) {
     if (is_array($xml['#']) && isset($xml['#']['FEEDBACK'][0]['#'])) {
         $feedbackxml = $xml['#']['FEEDBACK'][0]['#'];
 
+        // Detect some incorrect feedback combinations.
+        if ($result->getLevel() == 'required' and isset($feedbackxml['ON_CHECK'])) {
+            $result->setStatus(false);
+            $result->setErrorCode(INCORRECT_FEEDBACK_FOR_REQUIRED);
+        } else if ($result->getLevel() == 'optional' and isset($feedbackxml['ON_ERROR'])) {
+            $result->setStatus(false);
+            $result->setErrorCode(INCORRECT_FEEDBACK_FOR_OPTIONAL);
+        }
+
         if (!$result->status and $result->getLevel() == 'required') {
             if (isset($feedbackxml['ON_ERROR'][0]['@']['message'])) {
                 $result->setFeedbackStr($feedbackxml['ON_ERROR'][0]['@']['message']);