diff --git a/mod/assign/db/upgrade.php b/mod/assign/db/upgrade.php
index 0a1cb790c2e..3a6b3f4a67c 100644
--- a/mod/assign/db/upgrade.php
+++ b/mod/assign/db/upgrade.php
@@ -318,5 +318,18 @@ function xmldb_assign_upgrade($oldversion) {
         upgrade_mod_savepoint(true, 2017051501, 'assign');
     }
 
+    if ($oldversion < 2017051502) {
+        require_once($CFG->dirroot.'/mod/assign/upgradelib.php');
+        $brokenassigns = get_assignments_with_rescaled_null_grades();
+
+        // Set config value.
+        foreach ($brokenassigns as $assign) {
+            set_config('has_rescaled_null_grades_' . $assign, 1, 'assign');
+        }
+
+        // Main savepoint reached.
+        upgrade_mod_savepoint(true, 2017051502, 'assign');
+    }
+
     return true;
 }
diff --git a/mod/assign/lang/en/assign.php b/mod/assign/lang/en/assign.php
index 8b34a0f2eaa..5ca89772a59 100644
--- a/mod/assign/lang/en/assign.php
+++ b/mod/assign/lang/en/assign.php
@@ -196,6 +196,9 @@ $string['expandreviewpanel'] = 'Expand review panel';
 $string['extensionduedate'] = 'Extension due date';
 $string['extensionnotafterduedate'] = 'Extension date must be after the due date';
 $string['extensionnotafterfromdate'] = 'Extension date must be after the allow submissions from date';
+$string['fixrescalednullgrades'] = 'This assignment contains some erroneous grades. You can <a href="{$a->link}">automatically repair</a> these grades. This may affect course totals.';
+$string['fixrescalednullgradesconfirm'] = 'Are you sure you want to fix erroneous grades? All broken grades will be removed. This may affect course totals.';
+$string['fixrescalednullgradesdone'] = 'Grades fixed.';
 $string['gradecanbechanged'] = 'Grade can be changed';
 $string['gradersubmissionupdatedtext'] = '{$a->username} has updated their assignment submission
 for \'{$a->assignment}\' at {$a->timeupdated}
diff --git a/mod/assign/locallib.php b/mod/assign/locallib.php
index 0a9d8930942..30941e27e1a 100644
--- a/mod/assign/locallib.php
+++ b/mod/assign/locallib.php
@@ -600,6 +600,8 @@ class assign {
             $o .= $this->view_batch_markingallocation($mform);
         } else if ($action == 'viewsubmitforgradingerror') {
             $o .= $this->view_error_page(get_string('submitforgrading', 'assign'), $notices);
+        } else if ($action == 'fixrescalednullgrades') {
+            $o .= $this->view_fix_rescaled_null_grades();
         } else {
             $o .= $this->view_submission_page();
         }
@@ -4232,6 +4234,8 @@ class assign {
         $this->require_view_grades();
         require_once($CFG->dirroot . '/mod/assign/gradeform.php');
 
+        $this->add_grade_notices();
+
         // Only load this if it is.
         $o .= $this->view_grading_table();
 
@@ -5205,6 +5209,8 @@ class assign {
 
         $instance = $this->get_instance();
 
+        $this->add_grade_notices();
+
         $o = '';
 
         $postfix = '';
@@ -8538,6 +8544,92 @@ class assign {
         $completion = new completion_info($this->get_course());
         $completion->set_module_viewed($this->get_course_module());
     }
+
+    /**
+     * Checks for any grade notices, and adds notifications. Will display on assignment main page and grading table.
+     *
+     * @return void The notifications API will render the notifications at the appropriate part of the page.
+     */
+    protected function add_grade_notices() {
+        if (has_capability('mod/assign:grade', $this->get_context()) && get_config('assign', 'has_rescaled_null_grades_' . $this->get_instance()->id)) {
+            $link = new \moodle_url('/mod/assign/view.php', array('id' => $this->get_course_module()->id, 'action' => 'fixrescalednullgrades'));
+            \core\notification::warning(get_string('fixrescalednullgrades', 'mod_assign', ['link' => $link->out()]));
+        }
+    }
+
+    /**
+     * View fix rescaled null grades.
+     *
+     * @return bool True if null all grades are now fixed.
+     */
+    protected function fix_null_grades() {
+        global $DB;
+        $result = $DB->set_field_select(
+            'assign_grades',
+            'grade',
+            -1,
+            'grade <> ? AND grade < 0',
+            [-1]
+        );
+        $assign = clone $this->get_instance();
+        $assign->cmidnumber = $this->get_course_module()->idnumber;
+        assign_update_grades($assign);
+        return $result;
+    }
+
+    /**
+     * View fix rescaled null grades.
+     *
+     * @return void The notifications API will render the notifications at the appropriate part of the page.
+     */
+    protected function view_fix_rescaled_null_grades() {
+        global $OUTPUT;
+
+        $o = '';
+
+        require_capability('mod/assign:grade', $this->get_context());
+
+        $instance = $this->get_instance();
+
+        $o .= $this->get_renderer()->render(
+            new assign_header(
+                $instance,
+                $this->get_context(),
+                $this->show_intro(),
+                $this->get_course_module()->id
+            )
+        );
+
+        $confirm = optional_param('confirm', 0, PARAM_BOOL);
+
+        if ($confirm) {
+            confirm_sesskey();
+
+            // Fix the grades.
+            $this->fix_null_grades();
+            set_config('has_rescaled_null_grades_' . $instance->id, 0, 'assign');
+
+            // Display the notice.
+            $o .= $this->get_renderer()->notification(get_string('fixrescalednullgradesdone', 'assign'), 'notifysuccess');
+            $url = new moodle_url(
+                '/mod/assign/view.php',
+                array(
+                    'id' => $this->get_course_module()->id,
+                    'action' => 'grading'
+                )
+            );
+            $o .= $this->get_renderer()->continue_button($url);
+        } else {
+            // Ask for confirmation.
+            $continue = new \moodle_url('/mod/assign/view.php', array('id' => $this->get_course_module()->id, 'action' => 'fixrescalednullgrades', 'confirm' => true, 'sesskey' => sesskey()));
+            $cancel = new \moodle_url('/mod/assign/view.php', array('id' => $this->get_course_module()->id));
+            $o .= $OUTPUT->confirm(get_string('fixrescalednullgradesconfirm', 'mod_assign'), $continue, $cancel);
+        }
+
+        $o .= $this->view_footer();
+
+        return $o;
+    }
 }
 
 /**
diff --git a/mod/assign/tests/locallib_test.php b/mod/assign/tests/locallib_test.php
index 193f7fa0b65..884a68b4638 100644
--- a/mod/assign/tests/locallib_test.php
+++ b/mod/assign/tests/locallib_test.php
@@ -2953,4 +2953,147 @@ Anchor link 2:<a title=\"bananas\" href=\"../logo-240x60.gif\">Link text</a>
         $completiondata = $completion->get_data($cm, false, $student2->id);
         $this->assertEquals(1, $completiondata->completionstate);
     }
+
+    public function get_assignments_with_rescaled_null_grades_provider() {
+        return [
+            'Negative less than one is errant' => [
+                'grade' => -0.64,
+                'count' => 1,
+            ],
+            'Negative more than one is errant' => [
+                'grade' => -30.18,
+                'count' => 1,
+            ],
+            'Negative one exactly is not errant' => [
+                'grade' => -1,
+                'count' => 0,
+            ],
+            'Positive grade is not errant' => [
+                'grade' => 1,
+                'count' => 0,
+            ],
+            'Large grade is not errant' => [
+                'grade' => 100,
+                'count' => 0,
+            ],
+            'Zero grade is not errant' => [
+                'grade' => 0,
+                'count' => 0,
+            ],
+        ];
+    }
+
+    /**
+     * Test determining if the assignment as any null grades that were rescaled.
+     * @dataProvider get_assignments_with_rescaled_null_grades_provider
+     */
+    public function test_get_assignments_with_rescaled_null_grades($grade, $count) {
+        global $DB;
+
+        $this->resetAfterTest();
+
+        $assign = $this->create_instance(array('grade' => 100));
+
+        // Try getting a student's grade. This will give a grade of -1.
+        // Then we can override it with a bad negative grade.
+        $assign->get_user_grade($this->students[0]->id, true);
+
+        // Set the grade to something errant.
+        $DB->set_field(
+            'assign_grades',
+            'grade',
+            $grade,
+            [
+                'userid' => $this->students[0]->id,
+                'assignment' => $assign->get_instance()->id,
+            ]
+        );
+
+        $this->assertCount($count, get_assignments_with_rescaled_null_grades());
+    }
+
+    /**
+     * Data provider for test_fix_null_grades
+     * @return array[] Test data for test_fix_null_grades. Each element should contain grade, expectedcount and gradebookvalue
+     */
+    public function fix_null_grades_provider() {
+        return [
+            'Negative less than one is errant' => [
+                'grade' => -0.64,
+                'gradebookvalue' => null,
+            ],
+            'Negative more than one is errant' => [
+                'grade' => -30.18,
+                'gradebookvalue' => null,
+            ],
+            'Negative one exactly is not errant, but shouldn\'t be pushed to gradebook' => [
+                'grade' => -1,
+                'gradebookvalue' => null,
+            ],
+            'Positive grade is not errant' => [
+                'grade' => 1,
+                'gradebookvalue' => 1,
+            ],
+            'Large grade is not errant' => [
+                'grade' => 100,
+                'gradebookvalue' => 100,
+            ],
+            'Zero grade is not errant' => [
+                'grade' => 0,
+                'gradebookvalue' => 0,
+            ],
+        ];
+    }
+
+    /**
+     * Test fix_null_grades
+     * @param number $grade The grade we should set in the assign grading table.
+     * @param number $expectedcount The finalgrade we expect in the gradebook after fixing the grades.
+     * @dataProvider fix_null_grades_provider
+     */
+    public function test_fix_null_grades($grade, $gradebookvalue) {
+        global $DB;
+
+        $this->resetAfterTest();
+
+        $studentid = $this->students[0]->id;
+
+        $assign = $this->create_instance();
+
+        // Try getting a student's grade. This will give a grade of -1.
+        // Then we can override it with a bad negative grade.
+        $assign->get_user_grade($studentid, true);
+
+        // Set the grade to something errant.
+        $DB->set_field(
+            'assign_grades',
+            'grade',
+            $grade,
+            [
+                'userid' => $studentid,
+                'assignment' => $assign->get_instance()->id,
+            ]
+        );
+        $assign->grade = $grade;
+        $assigntemp = clone $assign->get_instance();
+        $assigntemp->cmidnumber = $assign->get_course_module()->idnumber;
+        assign_update_grades($assigntemp);
+
+        // Check that the gradebook was updated with the assign grade. So we can guarentee test results later on.
+        $expectedgrade = $grade == -1 ? null : $grade; // Assign sends null to the gradebook for -1 grades.
+        $gradegrade = grade_grade::fetch(array('userid' => $studentid, 'itemid' => $assign->get_grade_item()->id));
+        $this->assertEquals($expectedgrade, $gradegrade->rawgrade);
+
+        // Call fix_null_grades().
+        $method = new ReflectionMethod(assign::class, 'fix_null_grades');
+        $method->setAccessible(true);
+        $result = $method->invoke($assign);
+
+        $this->assertSame(true, $result);
+
+        $gradegrade = grade_grade::fetch(array('userid' => $studentid, 'itemid' => $assign->get_grade_item()->id));
+
+        // Check that the grade was updated in the gradebook by fix_null_grades.
+        $this->assertEquals($gradebookvalue, $gradegrade->finalgrade);
+    }
 }
diff --git a/mod/assign/upgradelib.php b/mod/assign/upgradelib.php
index c4fff773043..10ab600920a 100644
--- a/mod/assign/upgradelib.php
+++ b/mod/assign/upgradelib.php
@@ -414,3 +414,27 @@ class assign_upgrade_manager {
         return $newcm;
     }
 }
+
+/**
+ * Determines if the assignment as any null grades that were rescaled.
+ *
+ * Null grades are stored as -1 but should never be rescaled.
+ *
+ * @return int[] Array of the ids of all the assignments with rescaled null grades.
+ */
+function get_assignments_with_rescaled_null_grades() {
+    global $DB;
+
+    $query = 'SELECT id, assignment FROM {assign_grades}
+              WHERE grade < 0 AND grade <> -1';
+
+    $assignments = array_values($DB->get_records_sql($query));
+
+    $getassignmentid = function ($assignment) {
+        return $assignment->assignment;
+    };
+
+    $assignments = array_map($getassignmentid, $assignments);
+
+    return $assignments;
+}
diff --git a/mod/assign/version.php b/mod/assign/version.php
index 11c734888be..5ca85f4bac4 100644
--- a/mod/assign/version.php
+++ b/mod/assign/version.php
@@ -25,6 +25,6 @@
 defined('MOODLE_INTERNAL') || die();
 
 $plugin->component = 'mod_assign'; // Full name of the plugin (used for diagnostics).
-$plugin->version  = 2017051501;    // The current module version (Date: YYYYMMDDXX).
+$plugin->version  = 2017051502;    // The current module version (Date: YYYYMMDDXX).
 $plugin->requires = 2017050500;    // Requires this Moodle version.
 $plugin->cron     = 60;