diff --git a/mod/workshop/lang/en/workshop.php b/mod/workshop/lang/en/workshop.php
index 712208e6ccd..84bf166447d 100644
--- a/mod/workshop/lang/en/workshop.php
+++ b/mod/workshop/lang/en/workshop.php
@@ -50,6 +50,7 @@ $string['assessmentbyfullname'] = 'Assessment by {$a}';
 $string['assessmentbyyourself'] = 'Your assessment';
 $string['assessmentdeleted'] = 'Assessment deallocated';
 $string['assessmentend'] = 'Deadline for assessment';
+$string['assessmentendbeforestart'] = 'Deadline for assessment can not be specified before the open for assessment date';
 $string['assessmentenddatetime'] = 'Assessment deadline: {$a->daydatetime} ({$a->distanceday})';
 $string['assessmentform'] = 'Assessment form';
 $string['assessmentofsubmission'] = '<a href="{$a->assessmenturl}">Assessment</a> of <a href="{$a->submissionurl}">{$a->submissiontitle}</a>';
@@ -174,6 +175,7 @@ $string['participantreviewedby'] = 'Participant is reviewed by';
 $string['phaseassessment'] = 'Assessment phase';
 $string['phaseclosed'] = 'Closed';
 $string['phaseevaluation'] = 'Grading evaluation phase';
+$string['phasesoverlap'] = 'The submission phase and the assessment phase can not overlap';
 $string['phasesetup'] = 'Setup phase';
 $string['phasesubmission'] = 'Submission phase';
 $string['pluginadministration'] = 'Workshop administration';
@@ -207,6 +209,7 @@ $string['submissionby'] = 'Submission by {$a}';
 $string['submissionattachment'] = 'Attachment';
 $string['submissioncontent'] = 'Submission content';
 $string['submissionend'] = 'Submissions deadline';
+$string['submissionendbeforestart'] = 'Submissions deadline can not be specified before the open for submissions date';
 $string['submissionenddatetime'] = 'Submissions deadline: {$a->daydatetime} ({$a->distanceday})';
 $string['submissiongrade'] = 'Grade for submission';
 $string['submissiongrade_help'] = 'This setting specifies the maximum grade that may be obtained for submitted work.';
diff --git a/mod/workshop/mod_form.php b/mod/workshop/mod_form.php
index 74af6d4bbe1..078efe4a7d7 100644
--- a/mod/workshop/mod_form.php
+++ b/mod/workshop/mod_form.php
@@ -283,4 +283,42 @@ class mod_workshop_mod_form extends moodleform_mod {
 
         parent::definition_after_data();
     }
+
+    /**
+     * Validates the form input
+     *
+     * @param array $data submitted data
+     * @param array $files submitted files
+     * @return array eventual errors indexed by the field name
+     */
+    public function validation(array $data, array $files) {
+        $errors = array();
+
+        // check the phases borders are valid
+        if ($data['submissionstart'] > 0 and $data['submissionend'] > 0 and $data['submissionstart'] >= $data['submissionend']) {
+            $errors['submissionend'] = get_string('submissionendbeforestart', 'mod_workshop');
+        }
+        if ($data['assessmentstart'] > 0 and $data['assessmentend'] > 0 and $data['assessmentstart'] >= $data['assessmentend']) {
+            $errors['assessmentend'] = get_string('assessmentendbeforestart', 'mod_workshop');
+        }
+
+        // check the phases do not overlap
+        if (max($data['submissionstart'], $data['submissionend']) > 0 and max($data['assessmentstart'], $data['assessmentend']) > 0) {
+            $phasesubmissionend = max($data['submissionstart'], $data['submissionend']);
+            $phaseassessmentstart = min($data['assessmentstart'], $data['assessmentend']);
+            if ($phaseassessmentstart == 0) {
+                $phaseassessmentstart = max($data['assessmentstart'], $data['assessmentend']);
+            }
+            if ($phasesubmissionend > 0 and $phaseassessmentstart > 0 and $phaseassessmentstart < $phasesubmissionend) {
+                foreach (array('submissionend', 'submissionstart', 'assessmentstart', 'assessmentend') as $f) {
+                    if ($data[$f] > 0) {
+                        $errors[$f] = get_string('phasesoverlap', 'mod_workshop');
+                        break;
+                    }
+                }
+            }
+        }
+
+        return $errors;
+    }
 }