diff --git a/rector.php b/rector.php
index 9c3ad55d8..831914c78 100644
--- a/rector.php
+++ b/rector.php
@@ -14,5 +14,5 @@ return RectorConfig::configure()
     ])
     ->withImportNames(importShortClasses: false)
     ->withAttributesSets(doctrine: true)
-    ->withPhpSets(php71: true)
+    ->withPhpSets(php73: true)
     ->withTypeCoverageLevel(0);
diff --git a/src/Operator/PHP/Matches.php b/src/Operator/PHP/Matches.php
index 7d727bcae..0d3f2bfab 100644
--- a/src/Operator/PHP/Matches.php
+++ b/src/Operator/PHP/Matches.php
@@ -20,6 +20,6 @@ class Matches
             return false;
         }
 
-        return false !== stripos($subject, $pattern);
+        return false !== stripos($subject, (string) $pattern);
     }
 }
diff --git a/src/Operator/PHP/NotMatches.php b/src/Operator/PHP/NotMatches.php
index 9942a985f..49556815c 100644
--- a/src/Operator/PHP/NotMatches.php
+++ b/src/Operator/PHP/NotMatches.php
@@ -20,6 +20,6 @@ class NotMatches
             return true;
         }
 
-        return false === stripos($subject, $pattern);
+        return false === stripos($subject, (string) $pattern);
     }
 }