diff --git a/lib/datalib.php b/lib/datalib.php
index 53fbbfd4e9c..bf4b1548f0a 100644
--- a/lib/datalib.php
+++ b/lib/datalib.php
@@ -307,7 +307,7 @@ function table_column($table, $oldfield, $field, $type='integer', $size='10',
             if ($dbver >= '7.3') {
                 // modifying 'not null' is posible before 7.3
                 //update default values to table
-                if ($null == 'NOT NULL') {
+                if (strtoupper($null) == 'NOT NULL') {
                     execute_sql('UPDATE '. $CFG->prefix . $table .' SET '. $field .'='. $default .' WHERE '. $field .' IS NULL');
                     execute_sql('ALTER TABLE '. $CFG->prefix . $table .' ALTER COLUMN '. $field .' SET '. $null);
                 } else {