diff --git a/rules/CodingStyle/ClassNameImport/ClassNameImportSkipVoter/ClassLikeNameClassNameImportSkipVoter.php b/rules/CodingStyle/ClassNameImport/ClassNameImportSkipVoter/ClassLikeNameClassNameImportSkipVoter.php
index be8a44e9ce3..3cd5e4dec0d 100644
--- a/rules/CodingStyle/ClassNameImport/ClassNameImportSkipVoter/ClassLikeNameClassNameImportSkipVoter.php
+++ b/rules/CodingStyle/ClassNameImport/ClassNameImportSkipVoter/ClassLikeNameClassNameImportSkipVoter.php
@@ -46,8 +46,12 @@ public function shouldSkip(File $file, FullyQualifiedObjectType $fullyQualifiedO
         $namespace = strtolower((string) $namespace);
 
         $shortNameLowered = $fullyQualifiedObjectType->getShortNameLowered();
-        $subClassName = substr($fullyQualifiedObjectType->getClassName(), 0, -strlen($fullyQualifiedObjectType->getShortName()) - 1);
-        $fullyQualifiedObjectTypeNamespace = strtolower((string) $subClassName);
+        /**
+         * on php 7.x, substr() result can return false, so force (string) is needed
+         * @see https://github.com/rectorphp/rector-src/pull/7436
+         */
+        $subClassName = (string) substr($fullyQualifiedObjectType->getClassName(), 0, -strlen($fullyQualifiedObjectType->getShortName()) - 1);
+        $fullyQualifiedObjectTypeNamespace = strtolower($subClassName);
 
         foreach ($classLikeNames as $classLikeName) {
             if (strtolower($classLikeName) !== $shortNameLowered) {