diff --git a/examples/01-blog/Blog/Type/Scalar/UrlType.php b/examples/01-blog/Blog/Type/Scalar/UrlType.php
index c539121..0590546 100644
--- a/examples/01-blog/Blog/Type/Scalar/UrlType.php
+++ b/examples/01-blog/Blog/Type/Scalar/UrlType.php
@@ -30,11 +30,12 @@ class UrlType extends ScalarType
      *
      * @param mixed $value
      * @return mixed
+     * @throws Error
      */
     public function parseValue($value)
     {
         if (!is_string($value) || !filter_var($value, FILTER_VALIDATE_URL)) { // quite naive, but after all this is example
-            throw new \UnexpectedValueException("Cannot represent value as URL: " . Utils::printSafe($value));
+            throw new Error("Cannot represent value as URL: " . Utils::printSafe($value));
         }
         return $value;
     }
diff --git a/src/Executor/ExecutionResult.php b/src/Executor/ExecutionResult.php
index c9ec782..d998b96 100644
--- a/src/Executor/ExecutionResult.php
+++ b/src/Executor/ExecutionResult.php
@@ -1,7 +1,6 @@
 <?php
 namespace GraphQL\Executor;
 
-use GraphQL\Error\Error;
 use GraphQL\Error\FormattedError;
 
 /**
@@ -32,7 +31,7 @@ class ExecutionResult implements \JsonSerializable
      * @var \GraphQL\Error\Error[]
      */
     public $errors;
-    
+
     /**
      * User-defined serializable array of extensions included in serialized result.
      * Conforms to
@@ -138,7 +137,7 @@ class ExecutionResult implements \JsonSerializable
         if (null !== $this->data) {
             $result['data'] = $this->data;
         }
-        
+
         if (!empty($this->extensions)) {
             $result['extensions'] = (array) $this->extensions;
         }
diff --git a/src/Executor/Executor.php b/src/Executor/Executor.php
index fac9553..15098e0 100644
--- a/src/Executor/Executor.php
+++ b/src/Executor/Executor.php
@@ -1197,8 +1197,7 @@ class Executor
     }
 
     /**
-     * Complete a Scalar or Enum by serializing to a valid value, returning
-     * null if serialization is not possible.
+     * Complete a Scalar or Enum by serializing to a valid value, throwing if serialization is not possible.
      *
      * @param LeafType $returnType
      * @param $result
@@ -1207,14 +1206,21 @@ class Executor
      */
     private function completeLeafValue(LeafType $returnType, &$result)
     {
-        $serializedResult = $returnType->serialize($result);
-
-        if (Utils::isInvalid($serializedResult)) {
+        try {
+            return $returnType->serialize($result);
+        } catch (\Exception $error) {
             throw new InvariantViolation(
-                'Expected a value of type "'. Utils::printSafe($returnType) . '" but received: ' . Utils::printSafe($result)
+                'Expected a value of type "'. Utils::printSafe($returnType) . '" but received: ' . Utils::printSafe($result),
+                0,
+                $error
+            );
+        } catch (\Throwable $error) {
+            throw new InvariantViolation(
+                'Expected a value of type "'. Utils::printSafe($returnType) . '" but received: ' . Utils::printSafe($result),
+                0,
+                $error
             );
         }
-        return $serializedResult;
     }
 
     /**
diff --git a/src/Executor/Values.php b/src/Executor/Values.php
index c8353c4..372d63f 100644
--- a/src/Executor/Values.php
+++ b/src/Executor/Values.php
@@ -13,21 +13,16 @@ use GraphQL\Language\AST\NodeList;
 use GraphQL\Language\AST\VariableNode;
 use GraphQL\Language\AST\VariableDefinitionNode;
 use GraphQL\Language\Printer;
-use GraphQL\Type\Definition\EnumType;
-use GraphQL\Type\Definition\ScalarType;
 use GraphQL\Type\Schema;
 use GraphQL\Type\Definition\Directive;
 use GraphQL\Type\Definition\FieldDefinition;
-use GraphQL\Type\Definition\InputObjectType;
 use GraphQL\Type\Definition\InputType;
-use GraphQL\Type\Definition\ListOfType;
 use GraphQL\Type\Definition\NonNull;
 use GraphQL\Type\Definition\Type;
 use GraphQL\Utils\AST;
 use GraphQL\Utils\TypeInfo;
 use GraphQL\Utils\Utils;
 use GraphQL\Utils\Value;
-use GraphQL\Validator\DocumentValidator;
 
 class Values
 {
diff --git a/src/Language/AST/Node.php b/src/Language/AST/Node.php
index 6b42fe2..e12deec 100644
--- a/src/Language/AST/Node.php
+++ b/src/Language/AST/Node.php
@@ -1,7 +1,6 @@
 <?php
 namespace GraphQL\Language\AST;
 
-use GraphQL\Error\InvariantViolation;
 use GraphQL\Utils\Utils;
 
 abstract class Node
diff --git a/src/Type/Definition/BooleanType.php b/src/Type/Definition/BooleanType.php
index 2a1adc7..723990c 100644
--- a/src/Type/Definition/BooleanType.php
+++ b/src/Type/Definition/BooleanType.php
@@ -1,7 +1,9 @@
 <?php
 namespace GraphQL\Type\Definition;
 
+use GraphQL\Error\Error;
 use GraphQL\Language\AST\BooleanValueNode;
+use GraphQL\Language\AST\Node;
 use GraphQL\Utils\Utils;
 
 /**
@@ -32,22 +34,30 @@ class BooleanType extends ScalarType
     /**
      * @param mixed $value
      * @return bool
+     * @throws Error
      */
     public function parseValue($value)
     {
-        return is_bool($value) ? $value : Utils::undefined();
+        if (is_bool($value)) {
+            return $value;
+        }
+
+        throw new Error("Cannot represent value as boolean: " . Utils::printSafe($value));
     }
 
     /**
-     * @param $valueNode
+     * @param Node $valueNode
      * @param array|null $variables
      * @return bool|null
+     * @throws \Exception
      */
     public function parseLiteral($valueNode, array $variables = null)
     {
         if ($valueNode instanceof BooleanValueNode) {
             return (bool) $valueNode->value;
         }
-        return Utils::undefined();
+
+        // Intentionally without message, as all information already in wrapped Exception
+        throw new \Exception();
     }
 }
diff --git a/src/Type/Definition/CustomScalarType.php b/src/Type/Definition/CustomScalarType.php
index 14e1d53..5c25c8b 100644
--- a/src/Type/Definition/CustomScalarType.php
+++ b/src/Type/Definition/CustomScalarType.php
@@ -1,6 +1,7 @@
 <?php
 namespace GraphQL\Type\Definition;
 
+use GraphQL\Language\AST\Node;
 use GraphQL\Utils\AST;
 use GraphQL\Utils\Utils;
 
@@ -25,10 +26,6 @@ class CustomScalarType extends ScalarType
      */
     public function parseValue($value)
     {
-        if (Utils::isInvalid($value)) {
-            return Utils::undefined();
-        }
-
         if (isset($this->config['parseValue'])) {
             return call_user_func($this->config['parseValue'], $value);
         } else {
@@ -37,9 +34,10 @@ class CustomScalarType extends ScalarType
     }
 
     /**
-     * @param $valueNode
+     * @param Node $valueNode
      * @param array|null $variables
      * @return mixed
+     * @throws \Exception
      */
     public function parseLiteral(/* GraphQL\Language\AST\ValueNode */ $valueNode, array $variables = null)
     {
diff --git a/src/Type/Definition/EnumType.php b/src/Type/Definition/EnumType.php
index dbb7e33..08c02f1 100644
--- a/src/Type/Definition/EnumType.php
+++ b/src/Type/Definition/EnumType.php
@@ -1,6 +1,7 @@
 <?php
 namespace GraphQL\Type\Definition;
 
+use GraphQL\Error\Error;
 use GraphQL\Error\InvariantViolation;
 use GraphQL\Language\AST\EnumTypeDefinitionNode;
 use GraphQL\Language\AST\EnumValueNode;
@@ -103,7 +104,8 @@ class EnumType extends Type implements InputType, OutputType, LeafType, NamedTyp
 
     /**
      * @param $value
-     * @return null
+     * @return mixed
+     * @throws Error
      */
     public function serialize($value)
     {
@@ -112,36 +114,44 @@ class EnumType extends Type implements InputType, OutputType, LeafType, NamedTyp
             return $lookup[$value]->name;
         }
 
-        return Utils::undefined();
+        throw new Error("Cannot serialize value as enum: " . Utils::printSafe($value));
     }
 
     /**
      * @param $value
-     * @return null
+     * @return mixed
+     * @throws Error
      */
     public function parseValue($value)
     {
         $lookup = $this->getNameLookup();
-        return isset($lookup[$value]) ? $lookup[$value]->value : Utils::undefined();
+        if (isset($lookup[$value])) {
+            return $lookup[$value]->value;
+        }
+
+        throw new Error("Cannot represent value as enum: " . Utils::printSafe($value));
     }
 
     /**
-     * @param $value
+     * @param $valueNode
      * @param array|null $variables
      * @return null
+     * @throws \Exception
      */
-    public function parseLiteral($value, array $variables = null)
+    public function parseLiteral($valueNode, array $variables = null)
     {
-        if ($value instanceof EnumValueNode) {
+        if ($valueNode instanceof EnumValueNode) {
             $lookup = $this->getNameLookup();
-            if (isset($lookup[$value->value])) {
-                $enumValue = $lookup[$value->value];
+            if (isset($lookup[$valueNode->value])) {
+                $enumValue = $lookup[$valueNode->value];
                 if ($enumValue) {
                     return $enumValue->value;
                 }
             }
         }
-        return null;
+
+        // Intentionally without message, as all information already in wrapped Exception
+        throw new \Exception();
     }
 
     /**
diff --git a/src/Type/Definition/FloatType.php b/src/Type/Definition/FloatType.php
index e6391de..e04cd5a 100644
--- a/src/Type/Definition/FloatType.php
+++ b/src/Type/Definition/FloatType.php
@@ -49,13 +49,16 @@ values as specified by
      * @param $valueNode
      * @param array|null $variables
      * @return float|null
+     * @throws \Exception
      */
     public function parseLiteral($valueNode, array $variables = null)
     {
         if ($valueNode instanceof FloatValueNode || $valueNode instanceof IntValueNode) {
             return (float) $valueNode->value;
         }
-        return Utils::undefined();
+
+        // Intentionally without message, as all information already in wrapped Exception
+        throw new \Exception();
     }
 
     private function coerceFloat($value) {
diff --git a/src/Type/Definition/IDType.php b/src/Type/Definition/IDType.php
index d60a3a1..a35cf09 100644
--- a/src/Type/Definition/IDType.php
+++ b/src/Type/Definition/IDType.php
@@ -3,6 +3,7 @@ namespace GraphQL\Type\Definition;
 
 use GraphQL\Error\Error;
 use GraphQL\Language\AST\IntValueNode;
+use GraphQL\Language\AST\Node;
 use GraphQL\Language\AST\StringValueNode;
 use GraphQL\Utils\Utils;
 
@@ -30,6 +31,7 @@ When expected as an input type, any string (such as `"4"`) or integer
     /**
      * @param mixed $value
      * @return string
+     * @throws Error
      */
     public function serialize($value)
     {
@@ -51,22 +53,30 @@ When expected as an input type, any string (such as `"4"`) or integer
     /**
      * @param mixed $value
      * @return string
+     * @throws Error
      */
     public function parseValue($value)
     {
-        return (is_string($value) || is_int($value)) ? (string) $value : Utils::undefined();
+        if (is_string($value) || is_int($value)) {
+            return (string) $value;
+        }
+
+        throw new Error("Cannot represent value as ID: " . Utils::printSafe($value));
     }
 
     /**
-     * @param $ast
+     * @param Node $valueNode
      * @param array|null $variables
      * @return null|string
+     * @throws \Exception
      */
     public function parseLiteral($valueNode, array $variables = null)
     {
         if ($valueNode instanceof StringValueNode || $valueNode instanceof IntValueNode) {
             return $valueNode->value;
         }
-        return Utils::undefined();
+
+        // Intentionally without message, as all information already in wrapped Exception
+        throw new \Exception();
     }
 }
diff --git a/src/Type/Definition/IntType.php b/src/Type/Definition/IntType.php
index 0e401cf..3133aa2 100644
--- a/src/Type/Definition/IntType.php
+++ b/src/Type/Definition/IntType.php
@@ -55,6 +55,7 @@ values. Int can represent values between -(2^31) and 2^31 - 1. ';
      * @param $valueNode
      * @param array|null $variables
      * @return int|null
+     * @throws \Exception
      */
     public function parseLiteral($valueNode, array $variables = null)
     {
@@ -64,7 +65,9 @@ values. Int can represent values between -(2^31) and 2^31 - 1. ';
                 return $val;
             }
         }
-        return Utils::undefined();
+
+        // Intentionally without message, as all information already in wrapped Exception
+        throw new \Exception();
     }
 
     private function coerceInt($value) {
diff --git a/src/Type/Definition/LeafType.php b/src/Type/Definition/LeafType.php
index 9569b59..14ded04 100644
--- a/src/Type/Definition/LeafType.php
+++ b/src/Type/Definition/LeafType.php
@@ -1,6 +1,7 @@
 <?php
 namespace GraphQL\Type\Definition;
 
+use GraphQL\Error\Error;
 use \GraphQL\Language\AST\Node;
 
 /*
@@ -15,27 +16,30 @@ interface LeafType
      *
      * @param mixed $value
      * @return mixed
+     * @throws Error
      */
     public function serialize($value);
 
     /**
      * Parses an externally provided value (query variable) to use as an input
      *
-     * In the case of an invalid value this method must return Utils::undefined()
+     * In the case of an invalid value this method must throw an Exception
      *
      * @param mixed $value
      * @return mixed
+     * @throws Error
      */
     public function parseValue($value);
 
     /**
      * Parses an externally provided literal value (hardcoded in GraphQL query) to use as an input
      *
-     * In the case of an invalid value this method must return Utils::undefined()
+     * In the case of an invalid node or value this method must throw an Exception
      *
      * @param Node $valueNode
      * @param array|null $variables
      * @return mixed
+     * @throws \Exception
      */
     public function parseLiteral($valueNode, array $variables = null);
 }
diff --git a/src/Type/Definition/StringType.php b/src/Type/Definition/StringType.php
index a17bdcc..8de4063 100644
--- a/src/Type/Definition/StringType.php
+++ b/src/Type/Definition/StringType.php
@@ -60,13 +60,16 @@ represent free-form human-readable text.';
      * @param $valueNode
      * @param array|null $variables
      * @return null|string
+     * @throws \Exception
      */
     public function parseLiteral($valueNode, array $variables = null)
     {
         if ($valueNode instanceof StringValueNode) {
             return $valueNode->value;
         }
-        return Utils::undefined();
+
+        // Intentionally without message, as all information already in wrapped Exception
+        throw new \Exception();
     }
 
     private function coerceString($value) {
diff --git a/src/Type/Definition/Type.php b/src/Type/Definition/Type.php
index 5dd6b93..cf7ef2f 100644
--- a/src/Type/Definition/Type.php
+++ b/src/Type/Definition/Type.php
@@ -2,9 +2,6 @@
 namespace GraphQL\Type\Definition;
 
 use GraphQL\Error\InvariantViolation;
-use GraphQL\Language\AST\ListType;
-use GraphQL\Language\AST\NamedType;
-use GraphQL\Language\AST\NonNullType;
 use GraphQL\Language\AST\TypeDefinitionNode;
 use GraphQL\Type\Introspection;
 use GraphQL\Utils\Utils;
diff --git a/src/Type/EagerResolution.php b/src/Type/EagerResolution.php
index 262903c..d814868 100644
--- a/src/Type/EagerResolution.php
+++ b/src/Type/EagerResolution.php
@@ -2,13 +2,10 @@
 namespace GraphQL\Type;
 
 use GraphQL\Type\Definition\AbstractType;
-use GraphQL\Type\Definition\FieldArgument;
-use GraphQL\Type\Definition\InputObjectType;
 use GraphQL\Type\Definition\InterfaceType;
 use GraphQL\Type\Definition\ObjectType;
 use GraphQL\Type\Definition\Type;
 use GraphQL\Type\Definition\UnionType;
-use GraphQL\Type\Definition\WrappingType;
 use GraphQL\Utils\TypeInfo;
 use GraphQL\Utils\Utils;
 
diff --git a/src/Utils/AST.php b/src/Utils/AST.php
index 9a18915..7535239 100644
--- a/src/Utils/AST.php
+++ b/src/Utils/AST.php
@@ -28,7 +28,6 @@ use GraphQL\Type\Definition\EnumType;
 use GraphQL\Type\Definition\IDType;
 use GraphQL\Type\Definition\InputObjectType;
 use GraphQL\Type\Definition\InputType;
-use GraphQL\Type\Definition\LeafType;
 use GraphQL\Type\Definition\ListOfType;
 use GraphQL\Type\Definition\NonNull;
 use GraphQL\Type\Definition\ScalarType;
@@ -209,9 +208,18 @@ class AST
         if ($type instanceof ScalarType || $type instanceof EnumType) {
             // Since value is an internally represented value, it must be serialized
             // to an externally represented value before converting into an AST.
-            $serialized = $type->serialize($value);
-            if (null === $serialized || Utils::isInvalid($serialized)) {
-                return null;
+            try {
+                $serialized = $type->serialize($value);
+            } catch (\Exception $error) {
+                if ($error instanceof Error && $type instanceof EnumType) {
+                    return null;
+                }
+                throw $error;
+            } catch (\Throwable $error) {
+                if ($error instanceof Error && $type instanceof EnumType) {
+                    return null;
+                }
+                throw $error;
             }
 
             // Others serialize based on their corresponding PHP scalar types.
@@ -400,18 +408,12 @@ class AST
             // Invalid values represent a failure to parse correctly, in which case
             // no value is returned.
             try {
-                $result = $type->parseLiteral($valueNode, $variables);
+                return $type->parseLiteral($valueNode, $variables);
             } catch (\Exception $error) {
                 return $undefined;
             } catch (\Throwable $error) {
                 return $undefined;
             }
-
-            if (Utils::isInvalid($result)) {
-                return $undefined;
-            }
-
-            return $result;
         }
 
         throw new Error('Unknown type: ' . Utils::printSafe($type) . '.');
@@ -420,7 +422,7 @@ class AST
     /**
      * Produces a PHP value given a GraphQL Value AST.
      *
-     * Unlike `valueFromAST()`, no type is provided. The resulting JavaScript value
+     * Unlike `valueFromAST()`, no type is provided. The resulting PHP value
      * will reflect the provided GraphQL value AST.
      *
      * | GraphQL Value        | PHP Value     |
@@ -471,7 +473,7 @@ class AST
               );
             case $valueNode instanceof VariableNode:
                 $variableName = $valueNode->name->value;
-                return ($variables && isset($variables[$variableName]) && !Utils::isInvalid($variables[$variableName]))
+                return ($variables && isset($variables[$variableName]))
                     ? $variables[$variableName]
                     : null;
         }
diff --git a/src/Utils/Value.php b/src/Utils/Value.php
index 5606091..bf01018 100644
--- a/src/Utils/Value.php
+++ b/src/Utils/Value.php
@@ -46,14 +46,7 @@ class Value
             // throw to indicate failure. If it throws, maintain a reference to
             // the original error.
             try {
-                $parseResult = $type->parseValue($value);
-                if (Utils::isInvalid($parseResult)) {
-                    return self::ofErrors([
-                        self::coercionError("Expected type {$type->name}", $blameNode, $path),
-                    ]);
-                }
-
-                return self::ofValue($parseResult);
+                return self::ofValue($type->parseValue($value));
             } catch (\Exception $error) {
                 return self::ofErrors([
                     self::coercionError(
diff --git a/src/Validator/Rules/CustomValidationRule.php b/src/Validator/Rules/CustomValidationRule.php
index ba7cd40..5ccc606 100644
--- a/src/Validator/Rules/CustomValidationRule.php
+++ b/src/Validator/Rules/CustomValidationRule.php
@@ -1,7 +1,6 @@
 <?php
 namespace GraphQL\Validator\Rules;
 
-
 use GraphQL\Error\Error;
 use GraphQL\Validator\ValidationContext;
 
diff --git a/src/Validator/Rules/FieldsOnCorrectType.php b/src/Validator/Rules/FieldsOnCorrectType.php
index 7d052ae..1244a72 100644
--- a/src/Validator/Rules/FieldsOnCorrectType.php
+++ b/src/Validator/Rules/FieldsOnCorrectType.php
@@ -4,11 +4,9 @@ namespace GraphQL\Validator\Rules;
 use GraphQL\Error\Error;
 use GraphQL\Language\AST\FieldNode;
 use GraphQL\Language\AST\NodeKind;
-use GraphQL\Type\Definition\InputObjectType;
 use GraphQL\Type\Definition\InterfaceType;
 use GraphQL\Type\Definition\ObjectType;
 use GraphQL\Type\Definition\Type;
-use GraphQL\Type\Definition\UnionType;
 use GraphQL\Type\Schema;
 use GraphQL\Utils\Utils;
 use GraphQL\Validator\ValidationContext;
diff --git a/src/Validator/Rules/KnownFragmentNames.php b/src/Validator/Rules/KnownFragmentNames.php
index 35645db..ad5bc27 100644
--- a/src/Validator/Rules/KnownFragmentNames.php
+++ b/src/Validator/Rules/KnownFragmentNames.php
@@ -1,10 +1,8 @@
 <?php
 namespace GraphQL\Validator\Rules;
 
-
 use GraphQL\Error\Error;
 use GraphQL\Language\AST\FragmentSpreadNode;
-use GraphQL\Language\AST\Node;
 use GraphQL\Language\AST\NodeKind;
 use GraphQL\Validator\ValidationContext;
 
diff --git a/src/Validator/Rules/KnownTypeNames.php b/src/Validator/Rules/KnownTypeNames.php
index 47065c1..935b3ad 100644
--- a/src/Validator/Rules/KnownTypeNames.php
+++ b/src/Validator/Rules/KnownTypeNames.php
@@ -5,7 +5,6 @@ use GraphQL\Error\Error;
 use GraphQL\Language\AST\NamedTypeNode;
 use GraphQL\Language\AST\NodeKind;
 use GraphQL\Language\Visitor;
-use GraphQL\Type\Definition\Type;
 use GraphQL\Utils\Utils;
 use GraphQL\Validator\ValidationContext;
 
diff --git a/src/Validator/Rules/LoneAnonymousOperation.php b/src/Validator/Rules/LoneAnonymousOperation.php
index f02025f..7f848ef 100644
--- a/src/Validator/Rules/LoneAnonymousOperation.php
+++ b/src/Validator/Rules/LoneAnonymousOperation.php
@@ -3,7 +3,6 @@ namespace GraphQL\Validator\Rules;
 
 use GraphQL\Error\Error;
 use GraphQL\Language\AST\DocumentNode;
-use GraphQL\Language\AST\Node;
 use GraphQL\Language\AST\NodeKind;
 use GraphQL\Language\AST\OperationDefinitionNode;
 use GraphQL\Utils\Utils;
diff --git a/src/Validator/Rules/NoFragmentCycles.php b/src/Validator/Rules/NoFragmentCycles.php
index cf3eb0a..df81b77 100644
--- a/src/Validator/Rules/NoFragmentCycles.php
+++ b/src/Validator/Rules/NoFragmentCycles.php
@@ -1,11 +1,8 @@
 <?php
 namespace GraphQL\Validator\Rules;
 
-
 use GraphQL\Error\Error;
 use GraphQL\Language\AST\FragmentDefinitionNode;
-use GraphQL\Language\AST\FragmentSpreadNode;
-use GraphQL\Language\AST\Node;
 use GraphQL\Language\AST\NodeKind;
 use GraphQL\Language\Visitor;
 use GraphQL\Utils\Utils;
diff --git a/src/Validator/Rules/PossibleFragmentSpreads.php b/src/Validator/Rules/PossibleFragmentSpreads.php
index 37a24dc..0647e6f 100644
--- a/src/Validator/Rules/PossibleFragmentSpreads.php
+++ b/src/Validator/Rules/PossibleFragmentSpreads.php
@@ -1,7 +1,6 @@
 <?php
 namespace GraphQL\Validator\Rules;
 
-
 use GraphQL\Error\Error;
 use GraphQL\Language\AST\FragmentSpreadNode;
 use GraphQL\Language\AST\InlineFragmentNode;
diff --git a/src/Validator/Rules/ProvidedNonNullArguments.php b/src/Validator/Rules/ProvidedNonNullArguments.php
index a0370f9..4d0c63c 100644
--- a/src/Validator/Rules/ProvidedNonNullArguments.php
+++ b/src/Validator/Rules/ProvidedNonNullArguments.php
@@ -1,15 +1,12 @@
 <?php
 namespace GraphQL\Validator\Rules;
 
-
 use GraphQL\Error\Error;
 use GraphQL\Language\AST\DirectiveNode;
 use GraphQL\Language\AST\FieldNode;
-use GraphQL\Language\AST\Node;
 use GraphQL\Language\AST\NodeKind;
 use GraphQL\Language\Visitor;
 use GraphQL\Type\Definition\NonNull;
-use GraphQL\Utils\Utils;
 use GraphQL\Validator\ValidationContext;
 
 class ProvidedNonNullArguments extends AbstractValidationRule
diff --git a/src/Validator/Rules/QueryComplexity.php b/src/Validator/Rules/QueryComplexity.php
index 0b1d611..638010d 100644
--- a/src/Validator/Rules/QueryComplexity.php
+++ b/src/Validator/Rules/QueryComplexity.php
@@ -1,5 +1,4 @@
 <?php
-
 namespace GraphQL\Validator\Rules;
 
 use GraphQL\Error\Error;
diff --git a/src/Validator/Rules/UniqueFragmentNames.php b/src/Validator/Rules/UniqueFragmentNames.php
index af5706b..ebeb0b2 100644
--- a/src/Validator/Rules/UniqueFragmentNames.php
+++ b/src/Validator/Rules/UniqueFragmentNames.php
@@ -2,9 +2,7 @@
 namespace GraphQL\Validator\Rules;
 
 use GraphQL\Error\Error;
-use GraphQL\Language\AST\ArgumentNode;
 use GraphQL\Language\AST\FragmentDefinitionNode;
-use GraphQL\Language\AST\Node;
 use GraphQL\Language\AST\NodeKind;
 use GraphQL\Language\Visitor;
 use GraphQL\Validator\ValidationContext;
diff --git a/src/Validator/Rules/UniqueInputFieldNames.php b/src/Validator/Rules/UniqueInputFieldNames.php
index 3e60df8..1e48d48 100644
--- a/src/Validator/Rules/UniqueInputFieldNames.php
+++ b/src/Validator/Rules/UniqueInputFieldNames.php
@@ -2,7 +2,6 @@
 namespace GraphQL\Validator\Rules;
 
 use GraphQL\Error\Error;
-use GraphQL\Language\AST\Node;
 use GraphQL\Language\AST\NodeKind;
 use GraphQL\Language\AST\ObjectFieldNode;
 use GraphQL\Language\Visitor;
diff --git a/src/Validator/Rules/UniqueOperationNames.php b/src/Validator/Rules/UniqueOperationNames.php
index 17fff14..80a352c 100644
--- a/src/Validator/Rules/UniqueOperationNames.php
+++ b/src/Validator/Rules/UniqueOperationNames.php
@@ -2,7 +2,6 @@
 namespace GraphQL\Validator\Rules;
 
 use GraphQL\Error\Error;
-use GraphQL\Language\AST\Node;
 use GraphQL\Language\AST\NodeKind;
 use GraphQL\Language\AST\OperationDefinitionNode;
 use GraphQL\Language\Visitor;
diff --git a/src/Validator/Rules/UniqueVariableNames.php b/src/Validator/Rules/UniqueVariableNames.php
index cdbb1ca..4329721 100644
--- a/src/Validator/Rules/UniqueVariableNames.php
+++ b/src/Validator/Rules/UniqueVariableNames.php
@@ -2,7 +2,6 @@
 namespace GraphQL\Validator\Rules;
 
 use GraphQL\Error\Error;
-use GraphQL\Language\AST\Node;
 use GraphQL\Language\AST\NodeKind;
 use GraphQL\Language\AST\VariableDefinitionNode;
 use GraphQL\Validator\ValidationContext;
diff --git a/src/Validator/Rules/ValuesOfCorrectType.php b/src/Validator/Rules/ValuesOfCorrectType.php
index c77c93b..a64d034 100644
--- a/src/Validator/Rules/ValuesOfCorrectType.php
+++ b/src/Validator/Rules/ValuesOfCorrectType.php
@@ -173,20 +173,9 @@ class ValuesOfCorrectType extends AbstractValidationRule
         }
 
         // Scalars determine if a literal value is valid via parseLiteral() which
-        // may throw or return an invalid value to indicate failure.
+        // may throw to indicate failure.
         try {
-            $parseResult = $type->parseLiteral($node);
-            if (Utils::isInvalid($parseResult)) {
-                $context->reportError(
-                    new Error(
-                        self::badValueMessage(
-                            (string) $locationType,
-                            Printer::doPrint($node)
-                        ),
-                        $node
-                    )
-                );
-            }
+            $type->parseLiteral($node);
         } catch (\Exception $error) {
             // Ensure a reference to the original error is maintained.
             $context->reportError(
diff --git a/tests/Executor/TestClasses.php b/tests/Executor/TestClasses.php
index ef86938..0ae6ca6 100644
--- a/tests/Executor/TestClasses.php
+++ b/tests/Executor/TestClasses.php
@@ -1,6 +1,7 @@
 <?php
 namespace GraphQL\Tests\Executor;
 
+use GraphQL\Error\Error;
 use GraphQL\Type\Definition\ScalarType;
 use GraphQL\Utils\Utils;
 
@@ -53,28 +54,40 @@ class ComplexScalar extends ScalarType
 
     public $name = 'ComplexScalar';
 
+    /**
+     * {@inheritdoc}
+     */
     public function serialize($value)
     {
         if ($value === 'DeserializedValue') {
             return 'SerializedValue';
         }
-        return null;
+
+        throw new Error("Cannot serialize value as ComplexScalar: " . Utils::printSafe($value));
     }
 
+    /**
+     * {@inheritdoc}
+     */
     public function parseValue($value)
     {
         if ($value === 'SerializedValue') {
             return 'DeserializedValue';
         }
-        return Utils::undefined();
+
+        throw new Error("Cannot represent value as ComplexScalar: " . Utils::printSafe($value));
     }
 
+    /**
+     * {@inheritdoc}
+     */
     public function parseLiteral($valueNode, array $variables = null)
     {
         if ($valueNode->value === 'SerializedValue') {
             return 'DeserializedValue';
         }
-        return Utils::undefined();
+
+        throw new Error("Cannot represent literal as ComplexScalar: " . Utils::printSafe($valueNode->value));
     }
 }