diff --git a/phpstan-baseline.neon b/phpstan-baseline.neon
index 35d6267fc6..bdb1447c8a 100644
--- a/phpstan-baseline.neon
+++ b/phpstan-baseline.neon
@@ -1551,12 +1551,6 @@ parameters:
 			count: 2
 			path: src/Type/Php/LtrimFunctionReturnTypeExtension.php
 
-		-
-			message: '#^Doing instanceof PHPStan\\Type\\Constant\\ConstantStringType is error\-prone and deprecated\. Use Type\:\:getConstantStrings\(\) instead\.$#'
-			identifier: phpstanApi.instanceofType
-			count: 1
-			path: src/Type/Php/MbStrlenFunctionReturnTypeExtension.php
-
 		-
 			message: '#^Doing instanceof PHPStan\\Type\\Constant\\ConstantStringType is error\-prone and deprecated\. Use Type\:\:getConstantStrings\(\) instead\.$#'
 			identifier: phpstanApi.instanceofType
@@ -1641,12 +1635,6 @@ parameters:
 			count: 1
 			path: src/Type/Php/StrRepeatFunctionReturnTypeExtension.php
 
-		-
-			message: '#^Doing instanceof PHPStan\\Type\\Constant\\ConstantStringType is error\-prone and deprecated\. Use Type\:\:getConstantStrings\(\) instead\.$#'
-			identifier: phpstanApi.instanceofType
-			count: 1
-			path: src/Type/Php/StrlenFunctionReturnTypeExtension.php
-
 		-
 			message: '#^Doing instanceof PHPStan\\Type\\ObjectType is error\-prone and deprecated\. Use Type\:\:isObject\(\) or Type\:\:getObjectClassNames\(\) instead\.$#'
 			identifier: phpstanApi.instanceofType
diff --git a/src/Type/Php/MbStrlenFunctionReturnTypeExtension.php b/src/Type/Php/MbStrlenFunctionReturnTypeExtension.php
index 84464f30bd..8f6fd25819 100644
--- a/src/Type/Php/MbStrlenFunctionReturnTypeExtension.php
+++ b/src/Type/Php/MbStrlenFunctionReturnTypeExtension.php
@@ -92,24 +92,20 @@ public function getTypeFromFunctionCall(
 		}
 
 		$argType = $scope->getType($args[0]->value);
-		$constantScalars = $argType->getConstantScalarTypes();
+		$constantScalars = $argType->getConstantScalarValues();
 
 		$lengths = [];
 		foreach ($constantScalars as $constantScalar) {
-			$stringScalar = $constantScalar->toString();
-			if (!($stringScalar instanceof ConstantStringType)) {
-				$lengths = [];
-				break;
-			}
+			$stringScalar = (string) $constantScalar;
 
 			foreach ($encodings as $encoding) {
 				if (!$this->isSupportedEncoding($encoding)) {
 					continue;
 				}
 
-				$length = @mb_strlen($stringScalar->getValue(), $encoding);
+				$length = @mb_strlen($stringScalar, $encoding);
 				if ($length === false) {
-					throw new ShouldNotHappenException(sprintf('Got false on a supported encoding %s and value %s', $encoding, var_export($stringScalar->getValue(), true)));
+					throw new ShouldNotHappenException(sprintf('Got false on a supported encoding %s and value %s', $encoding, var_export($stringScalar, true)));
 				}
 				$lengths[] = $length;
 			}
diff --git a/src/Type/Php/StrlenFunctionReturnTypeExtension.php b/src/Type/Php/StrlenFunctionReturnTypeExtension.php
index 40b1c85587..bc91f8595b 100644
--- a/src/Type/Php/StrlenFunctionReturnTypeExtension.php
+++ b/src/Type/Php/StrlenFunctionReturnTypeExtension.php
@@ -6,7 +6,6 @@
 use PHPStan\Analyser\Scope;
 use PHPStan\Reflection\FunctionReflection;
 use PHPStan\Type\Constant\ConstantIntegerType;
-use PHPStan\Type\Constant\ConstantStringType;
 use PHPStan\Type\DynamicFunctionReturnTypeExtension;
 use PHPStan\Type\FloatType;
 use PHPStan\Type\IntegerRangeType;
@@ -42,16 +41,12 @@ public function getTypeFromFunctionCall(
 		}
 
 		$argType = $scope->getType($args[0]->value);
-		$constantScalars = $argType->getConstantScalarTypes();
+		$constantScalars = $argType->getConstantScalarValues();
 
 		$lengths = [];
 		foreach ($constantScalars as $constantScalar) {
-			$stringScalar = $constantScalar->toString();
-			if (!($stringScalar instanceof ConstantStringType)) {
-				$lengths = [];
-				break;
-			}
-			$length = strlen($stringScalar->getValue());
+			$stringScalar = (string) $constantScalar;
+			$length = strlen($stringScalar);
 			$lengths[] = $length;
 		}