diff --git a/rules-tests/CodeQuality/Rector/FuncCall/SimplifyRegexPatternRector/Fixture/slash_delimiter.php.inc b/rules-tests/CodeQuality/Rector/FuncCall/SimplifyRegexPatternRector/Fixture/slash_delimiter.php.inc
new file mode 100644
index 00000000000..36bac9c3f75
--- /dev/null
+++ b/rules-tests/CodeQuality/Rector/FuncCall/SimplifyRegexPatternRector/Fixture/slash_delimiter.php.inc
@@ -0,0 +1,27 @@
+<?php
+
+namespace Rector\Tests\CodeQuality\Rector\FuncCall\SimplifyRegexPatternRector\Fixture;
+
+class SlashDelimiter
+{
+    public function run(string $param)
+    {
+        return preg_match('/^[0-9]+$/', $param);
+    }
+}
+
+?>
+-----
+<?php
+
+namespace Rector\Tests\CodeQuality\Rector\FuncCall\SimplifyRegexPatternRector\Fixture;
+
+class SlashDelimiter
+{
+    public function run(string $param)
+    {
+        return preg_match('/^\d+$/', $param);
+    }
+}
+
+?>
diff --git a/rules/CodeQuality/Rector/FuncCall/SimplifyRegexPatternRector.php b/rules/CodeQuality/Rector/FuncCall/SimplifyRegexPatternRector.php
index 6c2d49ea604..4e599aa2fd6 100644
--- a/rules/CodeQuality/Rector/FuncCall/SimplifyRegexPatternRector.php
+++ b/rules/CodeQuality/Rector/FuncCall/SimplifyRegexPatternRector.php
@@ -21,12 +21,12 @@ final class SimplifyRegexPatternRector extends AbstractRector
      * @var array<string, string>
      */
     private const COMPLEX_PATTERN_TO_SIMPLE = [
-        '[0-9]' => '\d',
-        '[a-zA-Z0-9_]' => '\w',
-        '[A-Za-z0-9_]' => '\w',
-        '[0-9a-zA-Z_]' => '\w',
-        '[0-9A-Za-z_]' => '\w',
-        '[\r\n\t\f\v ]' => '\s',
+        '[0-9]' => '\\d',
+        '[a-zA-Z0-9_]' => '\\w',
+        '[A-Za-z0-9_]' => '\\w',
+        '[0-9a-zA-Z_]' => '\\w',
+        '[0-9A-Za-z_]' => '\\w',
+        '[\r\n\t\f\v ]' => '\\s',
     ];
 
     public function __construct(