diff --git a/lib/moodlelib.php b/lib/moodlelib.php
index 462aea614be..7eec95072fe 100644
--- a/lib/moodlelib.php
+++ b/lib/moodlelib.php
@@ -10572,52 +10572,33 @@ function get_course_display_name_for_list($course) {
  * Safe analogue of unserialize() that can only parse arrays
  *
  * Arrays may contain only integers or strings as both keys and values. Nested arrays are allowed.
- * Note: If any string (key or value) has semicolon (;) as part of the string parsing will fail.
- * This is a simple method to substitute unnecessary unserialize() in code and not intended to cover all possible cases.
  *
  * @param string $expression
  * @return array|bool either parsed array or false if parsing was impossible.
  */
 function unserialize_array($expression) {
-    $subs = [];
-    // Find nested arrays, parse them and store in $subs , substitute with special string.
-    while (preg_match('/([\^;\}])(a:\d+:\{[^\{\}]*\})/', $expression, $matches) && strlen($matches[2]) < strlen($expression)) {
-        $key = '--SUB' . count($subs) . '--';
-        $subs[$key] = unserialize_array($matches[2]);
-        if ($subs[$key] === false) {
-            return false;
-        }
-        $expression = str_replace($matches[2], $key . ';', $expression);
-    }
 
     // Check the expression is an array.
-    if (!preg_match('/^a:(\d+):\{([^\}]*)\}$/', $expression, $matches1)) {
+    if (!preg_match('/^a:(\d+):/', $expression)) {
         return false;
     }
-    // Get the size and elements of an array (key;value;key;value;....).
-    $parts = explode(';', $matches1[2]);
-    $size = intval($matches1[1]);
-    if (count($parts) < $size * 2 + 1) {
-        return false;
-    }
-    // Analyze each part and make sure it is an integer or string or a substitute.
-    $value = [];
-    for ($i = 0; $i < $size * 2; $i++) {
-        if (preg_match('/^i:(\d+)$/', $parts[$i], $matches2)) {
-            $parts[$i] = (int)$matches2[1];
-        } else if (preg_match('/^s:(\d+):"(.*)"$/', $parts[$i], $matches3) && strlen($matches3[2]) == (int)$matches3[1]) {
-            $parts[$i] = $matches3[2];
-        } else if (preg_match('/^--SUB\d+--$/', $parts[$i])) {
-            $parts[$i] = $subs[$parts[$i]];
-        } else {
-            return false;
+
+    $values = (array) unserialize_object($expression);
+
+    // Callback that returns true if the given value is an unserialized object, executes recursively.
+    $invalidvaluecallback = static function($value) use (&$invalidvaluecallback): bool {
+        if (is_array($value)) {
+            return (bool) array_filter($value, $invalidvaluecallback);
         }
+        return ($value instanceof stdClass) || ($value instanceof __PHP_Incomplete_Class);
+    };
+
+    // Iterate over the result to ensure there are no stray objects.
+    if (array_filter($values, $invalidvaluecallback)) {
+        return false;
     }
-    // Combine keys and values.
-    for ($i = 0; $i < $size * 2; $i += 2) {
-        $value[$parts[$i]] = $parts[$i+1];
-    }
-    return $value;
+
+    return $values;
 }
 
 /**
diff --git a/lib/tests/moodlelib_test.php b/lib/tests/moodlelib_test.php
index 1bdc12e732b..ccaa3f6bdcb 100644
--- a/lib/tests/moodlelib_test.php
+++ b/lib/tests/moodlelib_test.php
@@ -4621,24 +4621,26 @@ EOT;
     public function test_unserialize_array() {
         $a = [1, 2, 3];
         $this->assertEquals($a, unserialize_array(serialize($a)));
-        $this->assertEquals($a, unserialize_array(serialize($a)));
         $a = ['a' => 1, 2 => 2, 'b' => 'cde'];
         $this->assertEquals($a, unserialize_array(serialize($a)));
-        $this->assertEquals($a, unserialize_array(serialize($a)));
         $a = ['a' => 1, 2 => 2, 'b' => 'c"d"e'];
         $this->assertEquals($a, unserialize_array(serialize($a)));
         $a = ['a' => 1, 2 => ['c' => 'd', 'e' => 'f'], 'b' => 'cde'];
         $this->assertEquals($a, unserialize_array(serialize($a)));
-
-        // Can not unserialize if any string contains semicolons.
+        $a = ['a' => 1, 2 => ['c' => 'd', 'e' => ['f' => 'g']], 'b' => 'cde'];
+        $this->assertEquals($a, unserialize_array(serialize($a)));
         $a = ['a' => 1, 2 => 2, 'b' => 'c"d";e'];
-        $this->assertEquals(false, unserialize_array(serialize($a)));
+        $this->assertEquals($a, unserialize_array(serialize($a)));
 
         // Can not unserialize if there are any objects.
         $a = (object)['a' => 1, 2 => 2, 'b' => 'cde'];
-        $this->assertEquals(false, unserialize_array(serialize($a)));
+        $this->assertFalse(unserialize_array(serialize($a)));
         $a = ['a' => 1, 2 => 2, 'b' => (object)['a' => 'cde']];
-        $this->assertEquals(false, unserialize_array(serialize($a)));
+        $this->assertFalse(unserialize_array(serialize($a)));
+        $a = ['a' => 1, 2 => 2, 'b' => ['c' => (object)['a' => 'cde']]];
+        $this->assertFalse(unserialize_array(serialize($a)));
+        $a = ['a' => 1, 2 => 2, 'b' => ['c' => new lang_string('no')]];
+        $this->assertFalse(unserialize_array(serialize($a)));
 
         // Array used in the grader report.
         $a = array('aggregatesonly' => [51, 34], 'gradesonly' => [21, 45, 78]);