diff --git a/mod/assign/externallib.php b/mod/assign/externallib.php
index 6f0e4ee5c38..f2ab0750ab6 100644
--- a/mod/assign/externallib.php
+++ b/mod/assign/externallib.php
@@ -780,7 +780,7 @@ class mod_assign_external extends external_api {
                             'locked'           => new external_value(PARAM_INT, 'locked', VALUE_OPTIONAL),
                             'mailed'           => new external_value(PARAM_INT, 'mailed', VALUE_OPTIONAL),
                             'extensionduedate' => new external_value(PARAM_INT, 'extension due date', VALUE_OPTIONAL),
-                            'workflowstate'    => new external_value(PARAM_TEXT, 'marking workflow state', VALUE_OPTIONAL),
+                            'workflowstate'    => new external_value(PARAM_ALPHA, 'marking workflow state', VALUE_OPTIONAL),
                             'allocatedmarker'  => new external_value(PARAM_INT, 'allocated marker', VALUE_OPTIONAL)
                         )
                     )
@@ -1036,7 +1036,7 @@ class mod_assign_external extends external_api {
                             'locked'           => new external_value(PARAM_INT, 'locked'),
                             'mailed'           => new external_value(PARAM_INT, 'mailed'),
                             'extensionduedate' => new external_value(PARAM_INT, 'extension due date'),
-                            'workflowstate'    => new external_value(PARAM_TEXT, 'marking workflow state', VALUE_OPTIONAL),
+                            'workflowstate'    => new external_value(PARAM_ALPHA, 'marking workflow state', VALUE_OPTIONAL),
                             'allocatedmarker'  => new external_value(PARAM_INT, 'allocated marker')
                         )
                     )
diff --git a/mod/assign/locallib.php b/mod/assign/locallib.php
index cbf9535c0f5..482d5b53360 100644
--- a/mod/assign/locallib.php
+++ b/mod/assign/locallib.php
@@ -2212,7 +2212,7 @@ class assign {
         $o = '';
 
         $pluginsubtype = required_param('pluginsubtype', PARAM_ALPHA);
-        $plugintype = required_param('plugin', PARAM_TEXT);
+        $plugintype = required_param('plugin', PARAM_PLUGIN);
         $pluginaction = required_param('pluginaction', PARAM_ALPHA);
 
         $plugin = $this->get_plugin_by_type($pluginsubtype, $plugintype);
@@ -2268,7 +2268,7 @@ class assign {
 
         $submissionid = optional_param('sid', 0, PARAM_INT);
         $gradeid = optional_param('gid', 0, PARAM_INT);
-        $plugintype = required_param('plugin', PARAM_TEXT);
+        $plugintype = required_param('plugin', PARAM_PLUGIN);
         $item = null;
         if ($pluginsubtype == 'assignsubmission') {
             $plugin = $this->get_submission_plugin_by_type($plugintype);
@@ -5119,7 +5119,7 @@ class assign {
             $record->userid = $userid;
             if ($modified >= 0) {
                 $record->grade = unformat_float(optional_param('quickgrade_' . $record->userid, -1, PARAM_TEXT));
-                $record->workflowstate = optional_param('quickgrade_' . $record->userid.'_workflowstate', false, PARAM_TEXT);
+                $record->workflowstate = optional_param('quickgrade_' . $record->userid.'_workflowstate', false, PARAM_ALPHA);
                 $record->allocatedmarker = optional_param('quickgrade_' . $record->userid.'_allocatedmarker', false, PARAM_INT);
             } else {
                 // This user was not in the grading table.
@@ -6213,7 +6213,7 @@ class assign {
         $mform->setType('userid', PARAM_INT);
 
         $mform->addElement('hidden', 'action', 'savesubmission');
-        $mform->setType('action', PARAM_TEXT);
+        $mform->setType('action', PARAM_ALPHA);
     }
 
     /**
diff --git a/mod/assign/view.php b/mod/assign/view.php
index 9fa7e24395d..88fb5f8084d 100644
--- a/mod/assign/view.php
+++ b/mod/assign/view.php
@@ -28,7 +28,7 @@ require_once($CFG->dirroot . '/mod/assign/locallib.php');
 $id = required_param('id', PARAM_INT);
 
 $urlparams = array('id' => $id,
-                  'action' => optional_param('action', '', PARAM_TEXT),
+                  'action' => optional_param('action', '', PARAM_ALPHA),
                   'rownum' => optional_param('rownum', 0, PARAM_INT),
                   'useridlistid' => optional_param('action', 0, PARAM_INT));
 
@@ -50,4 +50,4 @@ $completion->set_module_viewed($cm);
 
 // Get the assign class to
 // render the page.
-echo $assign->view(optional_param('action', '', PARAM_TEXT));
+echo $assign->view(optional_param('action', '', PARAM_ALPHA));