diff --git a/lang/en/form.php b/lang/en/form.php
index e13d8b29086..2b9b10ab6c4 100644
--- a/lang/en/form.php
+++ b/lang/en/form.php
@@ -41,6 +41,7 @@ $string['err_nopunctuation'] = 'You must enter no punctuation characters here.';
 $string['err_numeric'] = 'You must enter a number here.';
 $string['err_rangelength'] = 'You must enter between {$a->format[0]} and {$a->format[1]} characters here.';
 $string['err_required'] = 'You must supply a value here.';
+$string['err_wrongfileextension'] = 'Some files ({$a->wrongfiles}) cannot be uploaded. Only file types {$a->whitelist} are allowed.';
 $string['filetypesany'] = 'All file types';
 $string['filetypesnotall'] = 'It is not allowed to select \'All file types\' here';
 $string['filetypesnotwhitelisted'] = 'These file types are not allowed here: {$a}';
diff --git a/lib/form/filemanager.php b/lib/form/filemanager.php
index 52657944d1e..93ff4cf83e3 100644
--- a/lib/form/filemanager.php
+++ b/lib/form/filemanager.php
@@ -308,6 +308,47 @@ class MoodleQuickForm_filemanager extends HTML_QuickForm_element implements temp
         $context['html'] = $this->toHtml();
         return $context;
     }
+
+    /**
+     * Check that all files have the allowed type.
+     *
+     * @param array $value Draft item id with the uploaded files.
+     * @return string|null Validation error message or null.
+     */
+    public function validateSubmitValue($value) {
+
+        $filetypesutil = new \core_form\filetypes_util();
+        $whitelist = $filetypesutil->normalize_file_types($this->_options['accepted_types']);
+
+        if (empty($whitelist) || $whitelist === ['*']) {
+            // Any file type is allowed, nothing to check here.
+            return;
+        }
+
+        $draftfiles = file_get_drafarea_files($value);
+        $wrongfiles = array();
+
+        if (empty($draftfiles)) {
+            // No file uploaded, nothing to check here.
+            return;
+        }
+
+        foreach ($draftfiles->list as $file) {
+            if (!$filetypesutil->is_allowed_file_type($file->filename, $whitelist)) {
+                $wrongfiles[] = $file->filename;
+            }
+        }
+
+        if ($wrongfiles) {
+            $a = array(
+                'whitelist' => implode(', ', $whitelist),
+                'wrongfiles' => implode(', ', $wrongfiles),
+            );
+            return get_string('err_wrongfileextension', 'core_form', $a);
+        }
+
+        return;
+    }
 }
 
 /**
diff --git a/lib/form/filepicker.php b/lib/form/filepicker.php
index 985879fd29d..c1485b2d586 100644
--- a/lib/form/filepicker.php
+++ b/lib/form/filepicker.php
@@ -230,4 +230,45 @@ class MoodleQuickForm_filepicker extends HTML_QuickForm_input implements templat
         $context['html'] = $this->toHtml();
         return $context;
     }
+
+    /**
+     * Check that the file has the allowed type.
+     *
+     * @param array $value Draft item id with the uploaded files.
+     * @return string|null Validation error message or null.
+     */
+    public function validateSubmitValue($value) {
+
+        $filetypesutil = new \core_form\filetypes_util();
+        $whitelist = $filetypesutil->normalize_file_types($this->_options['accepted_types']);
+
+        if (empty($whitelist) || $whitelist === ['*']) {
+            // Any file type is allowed, nothing to check here.
+            return;
+        }
+
+        $draftfiles = file_get_drafarea_files($value);
+        $wrongfiles = array();
+
+        if (empty($draftfiles)) {
+            // No file uploaded, nothing to check here.
+            return;
+        }
+
+        foreach ($draftfiles->list as $file) {
+            if (!$filetypesutil->is_allowed_file_type($file->filename, $whitelist)) {
+                $wrongfiles[] = $file->filename;
+            }
+        }
+
+        if ($wrongfiles) {
+            $a = array(
+                'whitelist' => implode(', ', $whitelist),
+                'wrongfiles' => implode(', ', $wrongfiles),
+            );
+            return get_string('err_wrongfileextension', 'core_form', $a);
+        }
+
+        return;
+    }
 }
diff --git a/lib/form/tests/behat/filetypes.feature b/lib/form/tests/behat/filetypes.feature
index cf75dd2b9b3..653e50d2b4d 100644
--- a/lib/form/tests/behat/filetypes.feature
+++ b/lib/form/tests/behat/filetypes.feature
@@ -34,4 +34,15 @@ Feature: There is a form element allowing to select filetypes
     Then I should see "Unknown file types: .doesnoexist"
     And I should see "These file types are not allowed here: .doc, .docx, .rtf"
     And I should see "It is not allowed to select 'All file types' here"
-    And I should not see "Unknown file types: .neverminditdoesnotexist"
\ No newline at end of file
+    And I should not see "Unknown file types: .neverminditdoesnotexist"
+
+  @javascript @_file_upload
+  Scenario: File manager element implicitly validates submitted files
+    # We can't directly upload the invalid file here as the upload repository would throw an exception.
+    # So instead we try to trick the filemanager, to be finally stopped by the implicit validation.
+    And I upload "lib/tests/fixtures/empty.txt" file to "Picky file manager" filemanager
+    And I follow "empty.txt"
+    And I set the field "Name" to "renamed.exe"
+    And I press "Update"
+    When I press "Save changes"
+    Then I should see "Some files (renamed.exe) cannot be uploaded. Only file types .txt are allowed."
diff --git a/lib/form/tests/fixtures/filetypes.php b/lib/form/tests/fixtures/filetypes.php
index 331fbfa7fe8..8477743c315 100644
--- a/lib/form/tests/fixtures/filetypes.php
+++ b/lib/form/tests/fixtures/filetypes.php
@@ -57,6 +57,8 @@ class test_form extends moodleform {
         $mform->addElement('filetypes', 'filetypes3', 'Unknown file types are allowed here',
             ['allowunknown' => true]);
 
+        $mform->addElement('filemanager', 'fileman1', 'Picky file manager', null, ['accepted_types' => '.txt']);
+
         $this->add_action_buttons(false);
     }
 }
diff --git a/mod/workshop/form/assessment_form.php b/mod/workshop/form/assessment_form.php
index 7ecbcf6738c..56128dcf5b3 100644
--- a/mod/workshop/form/assessment_form.php
+++ b/mod/workshop/form/assessment_form.php
@@ -120,41 +120,4 @@ class workshop_assessment_form extends moodleform {
     public function is_editable() {
         return !$this->_form->isFrozen();
     }
-
-    /**
-     * Validate assessment form data.
-     *
-     * @param array $data
-     * @param array $files
-     * @return array
-     */
-    public function validation($data, $files) {
-
-        $errors = parent::validation($data, $files);
-
-        if (isset($data['feedbackauthorattachment_filemanager']) and isset($this->workshop->overallfeedbackfiletypes)) {
-            $filetypesutil = new \core_form\filetypes_util();
-            $whitelist = $filetypesutil->normalize_file_types($this->workshop->overallfeedbackfiletypes);
-            if ($whitelist) {
-                $draftfiles = file_get_drafarea_files($data['feedbackauthorattachment_filemanager']);
-                if ($draftfiles) {
-                    $wrongfiles = array();
-                    foreach ($draftfiles->list as $file) {
-                        if (!$filetypesutil->is_allowed_file_type($file->filename, $whitelist)) {
-                            $wrongfiles[] = $file->filename;
-                        }
-                    }
-                    if ($wrongfiles) {
-                        $a = array(
-                            'whitelist' => implode(', ', $whitelist),
-                            'wrongfiles' => implode(', ', $wrongfiles),
-                        );
-                        $errors['feedbackauthorattachment_filemanager'] = get_string('err_wrongfileextension', 'mod_workshop', $a);
-                    }
-                }
-            }
-        }
-
-        return $errors;
-    }
 }
diff --git a/mod/workshop/lang/en/deprecated.txt b/mod/workshop/lang/en/deprecated.txt
index 01fea12c442..dc549a1c974 100644
--- a/mod/workshop/lang/en/deprecated.txt
+++ b/mod/workshop/lang/en/deprecated.txt
@@ -1,2 +1,3 @@
 err_unknownfileextension,mod_workshop
+err_wrongfileextension,mod_workshop
 yourassessment,mod_workshop
diff --git a/mod/workshop/lang/en/workshop.php b/mod/workshop/lang/en/workshop.php
index a87d615001e..ddaadc50c2c 100644
--- a/mod/workshop/lang/en/workshop.php
+++ b/mod/workshop/lang/en/workshop.php
@@ -107,7 +107,6 @@ $string['editingsubmission'] = 'Editing submission';
 $string['editsubmission'] = 'Edit submission';
 $string['err_multiplesubmissions'] = 'While editing this form, another version of the submission has been saved. Multiple submissions per user are not allowed.';
 $string['err_removegrademappings'] = 'Unable to remove the unused grade mappings';
-$string['err_wrongfileextension'] = 'Some files ({$a->wrongfiles}) cannot be uploaded. Only file types {$a->whitelist} are allowed.';
 $string['evaluategradeswait'] = 'Please wait until the assessments are evaluated and the grades are calculated';
 $string['evaluation'] = 'Grading evaluation';
 $string['evaluationmethod'] = 'Grading evaluation method';
@@ -375,3 +374,4 @@ $string['yourassessment'] = 'Your assessment';
 
 // Deprecated since Moodle 3.4.
 $string['err_unknownfileextension'] = 'Unknown file extension: {$a}';
+$string['err_wrongfileextension'] = 'Some files ({$a->wrongfiles}) cannot be uploaded. Only file types {$a->whitelist} are allowed.';
diff --git a/mod/workshop/submission_form.php b/mod/workshop/submission_form.php
index 6b794dcd935..29980feb374 100644
--- a/mod/workshop/submission_form.php
+++ b/mod/workshop/submission_form.php
@@ -94,29 +94,6 @@ class workshop_submission_form extends moodleform {
             $errors['attachment_filemanager'] = get_string('submissionrequiredfile', 'mod_workshop');
         }
 
-        if (isset($data['attachment_filemanager']) and isset($this->_customdata['workshop']->submissionfiletypes)) {
-            $filetypesutil = new \core_form\filetypes_util();
-            $whitelist = $filetypesutil->normalize_file_types($this->_customdata['workshop']->submissionfiletypes);
-            if ($whitelist) {
-                $draftfiles = file_get_drafarea_files($data['attachment_filemanager']);
-                if ($draftfiles) {
-                    $wrongfiles = array();
-                    foreach ($draftfiles->list as $file) {
-                        if (!$filetypesutil->is_allowed_file_type($file->filename, $whitelist)) {
-                            $wrongfiles[] = $file->filename;
-                        }
-                    }
-                    if ($wrongfiles) {
-                        $a = array(
-                            'whitelist' => implode(', ', $whitelist),
-                            'wrongfiles' => implode(', ', $wrongfiles),
-                        );
-                        $errors['attachment_filemanager'] = get_string('err_wrongfileextension', 'mod_workshop', $a);
-                    }
-                }
-            }
-        }
-
         return $errors;
     }
 }