diff --git a/mod/assign/lang/en/assign.php b/mod/assign/lang/en/assign.php
index a9896de2750..f1fff7da33c 100644
--- a/mod/assign/lang/en/assign.php
+++ b/mod/assign/lang/en/assign.php
@@ -175,6 +175,7 @@ $string['submissionempty'] = 'Nothing was submitted';
 $string['submissionmodified'] = 'You have existing submission data. Please leave this page and try again.';
 $string['submissionmodifiedgroup'] = 'The submission has been modified by somebody else. Please leave this page and try again.';
 $string['duedatereached'] = 'The due date for this assignment has now passed';
+$string['duedateaftersubmissionvalidation'] = 'Due date must be after the allow submissions from date.';
 $string['duedatevalidation'] = 'Due date cannot be earlier than the allow submissions from date.';
 $string['editattemptfeedback'] = 'Edit the grade and feedback for attempt number {$a}.';
 $string['editonline'] = 'Edit online';
diff --git a/mod/assign/mod_form.php b/mod/assign/mod_form.php
index 570587d7850..d936422c4cc 100644
--- a/mod/assign/mod_form.php
+++ b/mod/assign/mod_form.php
@@ -241,8 +241,8 @@ class mod_assign_mod_form extends moodleform_mod {
         $errors = parent::validation($data, $files);
 
         if (!empty($data['allowsubmissionsfromdate']) && !empty($data['duedate'])) {
-            if ($data['duedate'] < $data['allowsubmissionsfromdate']) {
-                $errors['duedate'] = get_string('duedatevalidation', 'assign');
+            if ($data['duedate'] <= $data['allowsubmissionsfromdate']) {
+                $errors['duedate'] = get_string('duedateaftersubmissionvalidation', 'assign');
             }
         }
         if (!empty($data['cutoffdate']) && !empty($data['duedate'])) {
diff --git a/mod/assign/override_form.php b/mod/assign/override_form.php
index 3c6620988cb..1ed1baeb45a 100644
--- a/mod/assign/override_form.php
+++ b/mod/assign/override_form.php
@@ -317,8 +317,8 @@ class assign_override_form extends moodleform {
         }
 
         if (!empty($data['allowsubmissionsfromdate']) && !empty($data['duedate'])) {
-            if ($data['duedate'] < $data['allowsubmissionsfromdate']) {
-                $errors['duedate'] = get_string('duedatevalidation', 'assign');
+            if ($data['duedate'] <= $data['allowsubmissionsfromdate']) {
+                $errors['duedate'] = get_string('duedateaftersubmissionvalidation', 'assign');
             }
         }