diff --git a/privacy/classes/local/request/contextlist.php b/privacy/classes/local/request/contextlist.php
index ea70cea8e04..4e391abcb75 100644
--- a/privacy/classes/local/request/contextlist.php
+++ b/privacy/classes/local/request/contextlist.php
@@ -48,28 +48,25 @@ class contextlist extends contextlist_base {
 
         $fields = \context_helper::get_preload_record_columns_sql('ctx');
         if ($fieldname = $this->guess_id_field_from_sql($sql)) {
-            if (is_int($fieldname)) {
+            if (is_numeric($fieldname)) {
                 $wrapper = "
-                    SELECT
-                        {$fields}
+                  SELECT {$fields}
                     FROM {context} ctx
                    WHERE ctx.id = :fieldvalue";
                 $params = ['fieldvalue' => $fieldname];
             } else {
                 // Able to guess a field name.
                 $wrapper = "
-                    SELECT
-                        {$fields}
+                  SELECT {$fields}
                     FROM {context} ctx
                     JOIN ({$sql}) target ON ctx.id = target.{$fieldname}";
             }
         } else {
             // No field name available. Fall back on a potentially slower version.
             $wrapper = "
-                SELECT
-                    {$fields}
+              SELECT {$fields}
                 FROM {context} ctx
-                WHERE ctx.id IN ({$sql})";
+               WHERE ctx.id IN ({$sql})";
         }
         $contexts = $DB->get_recordset_sql($wrapper, $params);
 
@@ -138,23 +135,24 @@ class contextlist extends contextlist_base {
      * Guess the name of the contextid field from the supplied SQL.
      *
      * @param   string  $sql The SQL to guess from
-     * @return  string  The field name.
+     * @return  string  The field name or a numeric value representing the context id
      */
     protected function guess_id_field_from_sql(string $sql) : string {
         // Get the list of relevant words from the SQL Query.
         // We explode the SQL by the space character, then trim any extra whitespace (e.g. newlines), before we filter
         // empty value, and finally we re-index the array.
-        $words = array_map('trim', explode(' ', $sql));
+        $sql = rtrim($sql, ';');
+        $words = array_map('trim', preg_split('/\s+/', $sql));
         $words = array_filter($words, function($word) {
             return $word !== '';
         });
         $words = array_values($words);
 
-        if ($firstfrom = array_search('FROM', $words)) {
+        if ($firstfrom = array_search('FROM', array_map('strtoupper', $words))) {
             // Found a FROM keyword.
             // Select the previous word.
             $fieldname = $words[$firstfrom - 1];
-            if (is_int($fieldname)) {
+            if (is_numeric($fieldname)) {
                 return $fieldname;
             }
 
@@ -164,6 +162,14 @@ class contextlist extends contextlist_base {
             }
 
             return $fieldname;
+
+        } else if ((count($words) == 1) && (is_numeric($words[0]))) {
+            // Not a real SQL, just a single numerical value - such as one returned by {@link self::add_system_context()}.
+            return $words[0];
+
+        } else if ((count($words) == 2) && (strtoupper($words[0]) === 'SELECT') && (is_numeric($words[1]))) {
+            // SQL returning a constant numerical value.
+            return $words[1];
         }
 
         return '';
diff --git a/privacy/tests/contextlist_test.php b/privacy/tests/contextlist_test.php
index 736e523ef5d..a247b3d3ab9 100644
--- a/privacy/tests/contextlist_test.php
+++ b/privacy/tests/contextlist_test.php
@@ -105,4 +105,85 @@ class contextlist_test extends advanced_testcase {
         $this->assertContains(\context_user::instance($user1->id)->id, $contexts);
         $this->assertContains(\context_user::instance($user2->id)->id, $contexts);
     }
+
+    /**
+     * Test {@link \core_privacy\local\request\contextlist::test_guess_id_field_from_sql()} implementation.
+     *
+     * @dataProvider data_guess_id_field_from_sql
+     * @param string $sql Input SQL we try to extract the context id field name from.
+     * @param string $expected Expected detected value.
+     */
+    public function test_guess_id_field_from_sql($sql, $expected) {
+
+        $rc = new \ReflectionClass(contextlist::class);
+        $rcm = $rc->getMethod('guess_id_field_from_sql');
+        $rcm->setAccessible(true);
+        $actual = $rcm->invoke(new contextlist(), $sql);
+
+        $this->assertEquals($expected, $actual, 'Unable to guess context id field in: '.$sql);
+    }
+
+    /**
+     * Provides data sets for {@link self::test_guess_id_field_from_sql()}.
+     *
+     * @return array
+     */
+    public function data_guess_id_field_from_sql() {
+        return [
+            'easy' => [
+                'SELECT contextid FROM {foo}',
+                'contextid',
+            ],
+            'with_distinct' => [
+                'SELECT DISTINCT contextid FROM {foo}',
+                'contextid',
+            ],
+            'with_dot' => [
+                'SELECT cx.id FROM {foo} JOIN {context} cx ON blahblahblah',
+                'id',
+            ],
+            'letter_case_does_not_matter' => [
+                'Select ctxid From {foo} Where bar = ?',
+                'ctxid',
+            ],
+            'alias' => [
+                'SELECT foo.contextid AS ctx FROM {bar} JOIN {foo} ON bar.id = foo.barid',
+                'ctx',
+            ],
+            'tabs' => [
+                "SELECT\tctxid\t\tFROM foo f",
+                'ctxid',
+            ],
+            'whitespace' => [
+                "SELECT
+                    ctxid\t
+                   \tFROM foo f",
+                'ctxid',
+            ],
+            'just_number' => [
+                '1',
+                '1',
+            ],
+            'select_number' => [
+                'SELECT 2',
+                '2',
+            ],
+            'select_number_with_semicolon' => [
+                'SELECT 3;',
+                '3',
+            ],
+            'select_number_from_table' => [
+                'SELECT 4 FROM users',
+                '4',
+            ],
+            'invalid_1' => [
+                'SELECT 1+1',
+                '',
+            ],
+            'invalid_2' => [
+                'muhehe',
+                '',
+            ],
+        ];
+    }
 }