diff --git a/phpstan-baseline.neon b/phpstan-baseline.neon
index 47101ea9fe..6410adeabf 100644
--- a/phpstan-baseline.neon
+++ b/phpstan-baseline.neon
@@ -1599,18 +1599,6 @@ parameters:
 			count: 2
 			path: src/Type/Php/IsSubclassOfFunctionTypeSpecifyingExtension.php
 
-		-
-			message: '#^Doing instanceof PHPStan\\Type\\ConstantScalarType is error\-prone and deprecated\. Use Type\:\:isConstantScalarValue\(\) or Type\:\:getConstantScalarTypes\(\) or Type\:\:getConstantScalarValues\(\) instead\.$#'
-			identifier: phpstanApi.instanceofType
-			count: 1
-			path: src/Type/Php/JsonThrowOnErrorDynamicReturnTypeExtension.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/JsonThrowOnErrorDynamicReturnTypeExtension.php
-
 		-
 			message: '#^Doing instanceof PHPStan\\Type\\Constant\\ConstantStringType is error\-prone and deprecated\. Use Type\:\:getConstantStrings\(\) instead\.$#'
 			identifier: phpstanApi.instanceofType
diff --git a/src/Type/Php/JsonThrowOnErrorDynamicReturnTypeExtension.php b/src/Type/Php/JsonThrowOnErrorDynamicReturnTypeExtension.php
index f9e551cc8a..79841125a0 100644
--- a/src/Type/Php/JsonThrowOnErrorDynamicReturnTypeExtension.php
+++ b/src/Type/Php/JsonThrowOnErrorDynamicReturnTypeExtension.php
@@ -12,12 +12,12 @@
 use PHPStan\Type\BitwiseFlagHelper;
 use PHPStan\Type\Constant\ConstantBooleanType;
 use PHPStan\Type\Constant\ConstantStringType;
-use PHPStan\Type\ConstantScalarType;
 use PHPStan\Type\ConstantTypeHelper;
 use PHPStan\Type\DynamicFunctionReturnTypeExtension;
 use PHPStan\Type\ObjectWithoutClassType;
 use PHPStan\Type\Type;
 use PHPStan\Type\TypeCombinator;
+use function count;
 use function is_bool;
 use function json_decode;
 
@@ -87,8 +87,14 @@ private function narrowTypeForJsonDecode(FuncCall $funcCall, Scope $scope, Type
 		}
 
 		$firstValueType = $scope->getType($args[0]->value);
-		if ($firstValueType instanceof ConstantStringType) {
-			return $this->resolveConstantStringType($firstValueType, $isForceArray);
+		if ($firstValueType->getConstantStrings() !== []) {
+			$types = [];
+
+			foreach ($firstValueType->getConstantStrings() as $constantString) {
+				$types[] = $this->resolveConstantStringType($constantString, $isForceArray);
+			}
+
+			return TypeCombinator::union(...$types);
 		}
 
 		if ($isForceArray) {
@@ -109,7 +115,7 @@ private function isForceArray(FuncCall $funcCall, Scope $scope): bool
 		}
 
 		$secondArgType = $scope->getType($args[1]->value);
-		$secondArgValue = $secondArgType instanceof ConstantScalarType ? $secondArgType->getValue() : null;
+		$secondArgValue = count($secondArgType->getConstantScalarValues()) === 1 ? $secondArgType->getConstantScalarValues()[0] : null;
 
 		if (is_bool($secondArgValue)) {
 			return $secondArgValue;
diff --git a/tests/PHPStan/Analyser/nsrt/json-decode/narrow_type.php b/tests/PHPStan/Analyser/nsrt/json-decode/narrow_type.php
index b00f971b56..a60f292a9f 100644
--- a/tests/PHPStan/Analyser/nsrt/json-decode/narrow_type.php
+++ b/tests/PHPStan/Analyser/nsrt/json-decode/narrow_type.php
@@ -32,3 +32,12 @@ function ($mixed) {
 	$value = json_decode($mixed, false);
 	assertType('mixed', $value);
 };
+
+function(string $json): void {
+	/** @var '{}'|'null' $json */
+	$value = json_decode($json);
+	assertType('stdClass|null', $value);
+
+	$value = json_decode($json, true);
+	assertType('array{}|null', $value);
+};