diff --git a/backup/util/helper/restore_log_rule.class.php b/backup/util/helper/restore_log_rule.class.php
index 6e182c019b1..9d3f61310c5 100644
--- a/backup/util/helper/restore_log_rule.class.php
+++ b/backup/util/helper/restore_log_rule.class.php
@@ -238,12 +238,12 @@ class restore_log_rule implements processable {
     protected function build_regexp($expression, $tokens) {
         // Replace to temp (and preg_quote() safe) placeholders
         foreach ($tokens as $token) {
-            $expression = preg_replace('~' . preg_quote($token, '~') . '~', '#@@#@@#', $expression, 1);
+            $expression = preg_replace('~' . preg_quote($token, '~') . '~', '%@@%@@%', $expression, 1);
         }
         // quote the expression
         $expression = preg_quote($expression, '~');
         // Replace all the placeholders
-        $expression = preg_replace('~#@@#@@#~', '(.*)', $expression);
+        $expression = preg_replace('~%@@%@@%~', '(.*)', $expression);
         return '~' . $expression . '~';
     }
 }
diff --git a/backup/util/helper/tests/restore_log_rule_test.php b/backup/util/helper/tests/restore_log_rule_test.php
index 03d016b0216..24d549bf134 100644
--- a/backup/util/helper/tests/restore_log_rule_test.php
+++ b/backup/util/helper/tests/restore_log_rule_test.php
@@ -49,4 +49,20 @@ class backup_restore_log_rule_testcase extends basic_testcase {
         // But the original log has been kept unmodified by the process() call.
         $this->assertEquals($originallog, $log);
     }
+
+    public function test_build_regexp() {
+        $original = 'Any (string) with [placeholders] like {this} and {this}. [end].';
+        $expectation = '~Any \(string\) with (.*) like (.*) and (.*)\. (.*)\.~';
+
+        $lr = new restore_log_rule('this', 'doesnt', 'matter', 'here');
+        $class = new ReflectionClass('restore_log_rule');
+
+        $method = $class->getMethod('extract_tokens');
+        $method->setAccessible(true);
+        $tokens = $method->invoke($lr, $original);
+
+        $method = $class->getMethod('build_regexp');
+        $method->setAccessible(true);
+        $this->assertSame($expectation, $method->invoke($lr, $original, $tokens));
+    }
 }
diff --git a/mod/lesson/pagetypes/shortanswer.php b/mod/lesson/pagetypes/shortanswer.php
index 62abed974c9..f59d94b1509 100644
--- a/mod/lesson/pagetypes/shortanswer.php
+++ b/mod/lesson/pagetypes/shortanswer.php
@@ -141,9 +141,9 @@ class lesson_page_type_shortanswer extends lesson_page {
                     $ignorecase = 'i';
                 }
             } else {
-                $expectedanswer = str_replace('*', '#####', $expectedanswer);
+                $expectedanswer = str_replace('*', '%@@%@@%', $expectedanswer);
                 $expectedanswer = preg_quote($expectedanswer, '/');
-                $expectedanswer = str_replace('#####', '.*', $expectedanswer);
+                $expectedanswer = str_replace('%@@%@@%', '.*', $expectedanswer);
             }
             // see if user typed in any of the correct answers
             if ((!$this->lesson->custom && $this->lesson->jumpto_is_correct($this->properties->id, $answer->jumpto)) or ($this->lesson->custom && $answer->score > 0) ) {