diff --git a/rector.php b/rector.php
index 375966c5c91..b24f7fe82f0 100644
--- a/rector.php
+++ b/rector.php
@@ -4,7 +4,6 @@
 
 use Rector\CodingStyle\Rector\String_\UseClassKeywordForClassNameResolutionRector;
 use Rector\Config\RectorConfig;
-use Rector\DeadCode\Rector\Cast\RecastingRemovalRector;
 use Rector\DeadCode\Rector\ConstFetch\RemovePhpVersionIdCheckRector;
 use Rector\Php55\Rector\String_\StringClassNameToClassConstantRector;
 
@@ -53,9 +52,4 @@
             __DIR__ . '/src/Configuration/RectorConfigBuilder.php',
             __DIR__ . '/src/Console/Notifier.php',
         ],
-
-        // todo: properly handle, substr() can return false on php 7.x
-        RecastingRemovalRector::class => [
-            __DIR__ . '/rules/CodingStyle/ClassNameImport/ClassNameImportSkipVoter/ClassLikeNameClassNameImportSkipVoter.php',
-        ],
     ]);
diff --git a/rules-tests/DeadCode/Rector/Cast/RecastingRemovalRector/Fixture/skip_substr.php.inc b/rules-tests/DeadCode/Rector/Cast/RecastingRemovalRector/Fixture/skip_substr.php.inc
new file mode 100644
index 00000000000..07f63228bfb
--- /dev/null
+++ b/rules-tests/DeadCode/Rector/Cast/RecastingRemovalRector/Fixture/skip_substr.php.inc
@@ -0,0 +1,17 @@
+<?php
+
+namespace Rector\Tests\DeadCode\Rector\Cast\RecastingRemovalRector\Fixture;
+
+/**
+ * On PHP 7.4, substr() can returns false
+ */
+class SkipSubstr
+{
+    public function run(): string
+    {
+        $className = 'Exception';
+        return (string) substr($className, 0, -strlen($className) - 1);
+    }
+}
+
+?>
diff --git a/rules-tests/TypeDeclaration/Rector/ClassMethod/ReturnUnionTypeRector/Fixture/true_in_union_become_bool.php.inc b/rules-tests/TypeDeclaration/Rector/ClassMethod/ReturnUnionTypeRector/Fixture/true_in_union_become_bool.php.inc
index a766298d571..624d4ff8f7d 100644
--- a/rules-tests/TypeDeclaration/Rector/ClassMethod/ReturnUnionTypeRector/Fixture/true_in_union_become_bool.php.inc
+++ b/rules-tests/TypeDeclaration/Rector/ClassMethod/ReturnUnionTypeRector/Fixture/true_in_union_become_bool.php.inc
@@ -13,7 +13,7 @@ final class TrueInUnionBecomeBool
             return true;
         }
 
-        return substr('warning', 1);
+        return strtoupper('warning');
     }
 }
 
@@ -34,7 +34,7 @@ final class TrueInUnionBecomeBool
             return true;
         }
 
-        return substr('warning', 1);
+        return strtoupper('warning');
     }
 }
 
diff --git a/rules-tests/TypeDeclaration/Rector/ClassMethod/ReturnUnionTypeRector/FixtureTrueInUnion/true_in_union.php.inc b/rules-tests/TypeDeclaration/Rector/ClassMethod/ReturnUnionTypeRector/FixtureTrueInUnion/true_in_union.php.inc
index db2839b5ad0..880dfafd56e 100644
--- a/rules-tests/TypeDeclaration/Rector/ClassMethod/ReturnUnionTypeRector/FixtureTrueInUnion/true_in_union.php.inc
+++ b/rules-tests/TypeDeclaration/Rector/ClassMethod/ReturnUnionTypeRector/FixtureTrueInUnion/true_in_union.php.inc
@@ -13,7 +13,7 @@ final class TrueInUnion
             return true;
         }
 
-        return substr('warning', 1);
+        return strtoupper('warning');
     }
 }
 
@@ -34,7 +34,7 @@ final class TrueInUnion
             return true;
         }
 
-        return substr('warning', 1);
+        return strtoupper('warning');
     }
 }
 
diff --git a/src/NodeTypeResolver/NodeTypeResolver.php b/src/NodeTypeResolver/NodeTypeResolver.php
index 6cde992ec83..ea9ddec9ac7 100644
--- a/src/NodeTypeResolver/NodeTypeResolver.php
+++ b/src/NodeTypeResolver/NodeTypeResolver.php
@@ -39,6 +39,7 @@
 use PHPStan\Type\NullType;
 use PHPStan\Type\ObjectType;
 use PHPStan\Type\ObjectWithoutClassType;
+use PHPStan\Type\StringType;
 use PHPStan\Type\ThisType;
 use PHPStan\Type\Type;
 use PHPStan\Type\TypeCombinator;
@@ -620,6 +621,11 @@ private function resolveNativeTypeWithBuiltinMethodCallFallback(Expr $expr, Scop
                 return $scope->getNativeType($expr);
             }
 
+            // substr can return false on php 7.x
+            if ($this->nodeNameResolver->isName($expr, 'substr') && ! $expr->isFirstClassCallable()) {
+                return new UnionType([new StringType(), new ConstantBooleanType(false)]);
+            }
+
             return $scope->getType($expr);
         }