diff --git a/docs/reference.md b/docs/reference.md
index 1f86412..789eb5f 100644
--- a/docs/reference.md
+++ b/docs/reference.md
@@ -936,7 +936,12 @@ const UNION_TYPE_DEFINITION = "UnionTypeDefinition";
 const ENUM_TYPE_DEFINITION = "EnumTypeDefinition";
 const ENUM_VALUE_DEFINITION = "EnumValueDefinition";
 const INPUT_OBJECT_TYPE_DEFINITION = "InputObjectTypeDefinition";
+const SCALAR_TYPE_EXTENSION = "ScalarTypeExtension";
 const OBJECT_TYPE_EXTENSION = "ObjectTypeExtension";
+const INTERFACE_TYPE_EXTENSION = "InterfaceTypeExtension";
+const UNION_TYPE_EXTENSION = "UnionTypeExtension";
+const ENUM_TYPE_EXTENSION = "EnumTypeExtension";
+const INPUT_OBJECT_TYPE_EXTENSION = "InputObjectTypeExtension";
 const DIRECTIVE_DEFINITION = "DirectiveDefinition";
 ```
 
diff --git a/src/Executor/Values.php b/src/Executor/Values.php
index 49bcc3a..0644db0 100644
--- a/src/Executor/Values.php
+++ b/src/Executor/Values.php
@@ -273,31 +273,36 @@ class Values
             return $errors;
         }
 
-        Utils::invariant($type instanceof EnumType || $type instanceof ScalarType, 'Must be input type');
-
-
-        try {
-            // Scalar/Enum input checks to ensure the type can parse the value to
-            // a non-null value.
-
-            if (!$type->isValidValue($value)) {
-                $v = Utils::printSafeJson($value);
-                return [
-                    "Expected type \"{$type->name}\", found $v."
-                ];
+        if ($type instanceof EnumType) {
+            if (!is_string($value) || !$type->getValue($value)) {
+                $printed = Utils::printSafeJson($value);
+                return ["Expected type \"{$type->name}\", found $printed."];
             }
-        } catch (\Exception $e) {
-            return [
-                "Expected type \"{$type->name}\", found " . Utils::printSafeJson($value) . ': ' .
-                $e->getMessage()
-            ];
-        } catch (\Throwable $e) {
-            return [
-                "Expected type \"{$type->name}\", found " . Utils::printSafeJson($value) . ': ' .
-                $e->getMessage()
-            ];
+
+            return [];
         }
 
+        Utils::invariant($type instanceof ScalarType, 'Must be a scalar type');
+        /** @var ScalarType $type */
+
+        // Scalars determine if a value is valid via parseValue().
+        try {
+            $parseResult = $type->parseValue($value);
+            if (Utils::isInvalid($parseResult)) {
+                $printed = Utils::printSafeJson($value);
+                return [
+                    "Expected type \"{$type->name}\", found $printed."
+                ];
+            }
+        } catch (\Exception $error) {
+            $printed = Utils::printSafeJson($value);
+            $message = $error->getMessage();
+            return ["Expected type \"{$type->name}\", found $printed; $message"];
+        } catch (\Throwable $error) {
+            $printed = Utils::printSafeJson($value);
+            $message = $error->getMessage();
+            return ["Expected type \"{$type->name}\", found $printed; $message"];
+        }
 
         return [];
     }
@@ -370,12 +375,34 @@ class Values
             return $coercedObj;
         }
 
-        Utils::invariant($type instanceof EnumType || $type instanceof ScalarType, 'Must be input type');
+        if ($type instanceof EnumType) {
+            if (!is_string($value) || !$type->getValue($value)) {
+                return $undefined;
+            }
 
-        if ($type->isValidValue($value)) {
-            return $type->parseValue($value);
+            $enumValue = $type->getValue($value);
+            if (!$enumValue) {
+                return $undefined;
+            }
+
+            return $enumValue->value;
         }
 
-        return $undefined;
+        Utils::invariant($type instanceof ScalarType, 'Must be a scalar type');
+        /** @var ScalarType $type */
+
+        // Scalars determine if a value is valid via parseValue().
+        try {
+            $parseResult = $type->parseValue($value);
+            if (Utils::isInvalid($parseResult)) {
+                return $undefined;
+            }
+        } catch (\Exception $error) {
+            return $undefined;
+        } catch (\Throwable $error) {
+            return $undefined;
+        }
+
+        return $parseResult;
     }
 }
diff --git a/src/Type/Definition/EnumType.php b/src/Type/Definition/EnumType.php
index 1f18875..0019d24 100644
--- a/src/Type/Definition/EnumType.php
+++ b/src/Type/Definition/EnumType.php
@@ -115,25 +115,6 @@ class EnumType extends Type implements InputType, OutputType, LeafType
         return Utils::undefined();
     }
 
-    /**
-     * @param string $value
-     * @return bool
-     */
-    public function isValidValue($value)
-    {
-        return is_string($value) && $this->getNameLookup()->offsetExists($value);
-    }
-
-    /**
-     * @param $valueNode
-     * @param array|null $variables
-     * @return bool
-     */
-    public function isValidLiteral($valueNode, array $variables = null)
-    {
-        return $valueNode instanceof EnumValueNode && $this->getNameLookup()->offsetExists($valueNode->value);
-    }
-
     /**
      * @param $value
      * @return null
diff --git a/src/Type/Definition/LeafType.php b/src/Type/Definition/LeafType.php
index 2ec8efc..9569b59 100644
--- a/src/Type/Definition/LeafType.php
+++ b/src/Type/Definition/LeafType.php
@@ -38,17 +38,4 @@ interface LeafType
      * @return mixed
      */
     public function parseLiteral($valueNode, array $variables = null);
-
-    /**
-     * @param string $value
-     * @return bool
-     */
-    public function isValidValue($value);
-
-    /**
-     * @param Node $valueNode
-     * @param array|null $variables
-     * @return bool
-     */
-    public function isValidLiteral($valueNode, array $variables = null);
 }
diff --git a/src/Type/Definition/ScalarType.php b/src/Type/Definition/ScalarType.php
index bc485b5..6038796 100644
--- a/src/Type/Definition/ScalarType.php
+++ b/src/Type/Definition/ScalarType.php
@@ -38,28 +38,4 @@ abstract class ScalarType extends Type implements OutputType, InputType, LeafTyp
 
         Utils::assertValidName($this->name);
     }
-
-    /**
-     * Determines if an internal value is valid for this type.
-     *
-     * @param $value
-     * @return bool
-     */
-    public function isValidValue($value)
-    {
-        return !Utils::isInvalid($this->parseValue($value));
-    }
-
-    /**
-     * Determines if an internal value is valid for this type.
-     * Equivalent to checking for if the parsedLiteral is nullish.
-     *
-     * @param $valueNode
-     * @param array|null $variables
-     * @return bool
-     */
-    public function isValidLiteral($valueNode, array $variables = null)
-    {
-        return !Utils::isInvalid($this->parseLiteral($valueNode, $variables));
-    }
 }
diff --git a/src/Utils/AST.php b/src/Utils/AST.php
index ea38aa4..d5c867e 100644
--- a/src/Utils/AST.php
+++ b/src/Utils/AST.php
@@ -383,15 +383,37 @@ class AST
             return $coercedObj;
         }
 
-        if (!$type instanceof ScalarType && !$type instanceof EnumType) {
-            throw new InvariantViolation('Must be input type');
+        if ($type instanceof EnumType) {
+            if (!$valueNode instanceof EnumValueNode) {
+                return $undefined;
+            }
+            $enumValue = $type->getValue($valueNode->value);
+            if (!$enumValue) {
+                return $undefined;
+            }
+
+            return $enumValue->value;
         }
 
-        if ($type->isValidLiteral($valueNode, $variables)) {
-            return $type->parseLiteral($valueNode, $variables);
+        Utils::invariant($type instanceof ScalarType, 'Must be scalar type');
+        /** @var ScalarType $type */
+
+        // Scalars fulfill parsing a literal value via parseLiteral().
+        // Invalid values represent a failure to parse correctly, in which case
+        // no value is returned.
+        try {
+            $result = $type->parseLiteral($valueNode, $variables);
+        } catch (\Exception $error) {
+            return $undefined;
+        } catch (\Throwable $error) {
+            return $undefined;
         }
 
-        return $undefined;
+        if (Utils::isInvalid($result)) {
+            return $undefined;
+        }
+
+        return $result;
     }
 
     /**
diff --git a/src/Validator/DocumentValidator.php b/src/Validator/DocumentValidator.php
index 2b6e242..cf7f30c 100644
--- a/src/Validator/DocumentValidator.php
+++ b/src/Validator/DocumentValidator.php
@@ -2,6 +2,7 @@
 namespace GraphQL\Validator;
 
 use GraphQL\Error\Error;
+use GraphQL\Language\AST\EnumValueNode;
 use GraphQL\Language\AST\ListValueNode;
 use GraphQL\Language\AST\DocumentNode;
 use GraphQL\Language\AST\NodeKind;
@@ -309,12 +310,33 @@ class DocumentValidator
             return $errors;
         }
 
-        Utils::invariant($type instanceof ScalarType || $type instanceof EnumType, 'Must be input type');
+        if ($type instanceof EnumType) {
+            if (!$valueNode instanceof EnumValueNode || !$type->getValue($valueNode->value)) {
+                $printed = Printer::doPrint($valueNode);
+                return ["Expected type \"{$type->name}\", found $printed."];
+            }
 
-        // Scalars determine if a literal values is valid.
-        if (!$type->isValidLiteral($valueNode)) {
+            return [];
+        }
+
+        Utils::invariant($type instanceof ScalarType, 'Must be a scalar type');
+        /** @var ScalarType $type */
+
+        // Scalars determine if a literal values is valid via parseLiteral().
+        try {
+            $parseResult = $type->parseLiteral($valueNode);
+            if (Utils::isInvalid($parseResult)) {
+                $printed = Printer::doPrint($valueNode);
+                return ["Expected type \"{$type->name}\", found $printed."];
+            }
+        } catch (\Exception $error) {
             $printed = Printer::doPrint($valueNode);
-            return [ "Expected type \"{$type->name}\", found $printed." ];
+            $message = $error->getMessage();
+            return ["Expected type \"{$type->name}\", found $printed; $message"];
+        } catch (\Throwable $error) {
+            $printed = Printer::doPrint($valueNode);
+            $message = $error->getMessage();
+            return ["Expected type \"{$type->name}\", found $printed; $message"];
         }
 
         return [];
diff --git a/tests/Validator/TestCase.php b/tests/Validator/TestCase.php
index 028ac24..770e650 100644
--- a/tests/Validator/TestCase.php
+++ b/tests/Validator/TestCase.php
@@ -260,17 +260,6 @@ abstract class TestCase extends \PHPUnit_Framework_TestCase
             ]
         ]);
 
-        $invalidScalar = new CustomScalarType([
-            'name' => 'Invalid',
-            'serialize' => function ($value) { return $value; },
-            'parseLiteral' => function ($node) {
-                throw new \Exception('Invalid scalar is always invalid: ' . $node->value);
-            },
-            'parseValue' => function ($value) {
-                throw new \Exception('Invalid scalar is always invalid: ' . $value);
-            },
-        ]);
-
         $anyScalar = new CustomScalarType([
             'name' => 'Any',
             'serialize' => function ($value) { return $value; },
@@ -278,6 +267,19 @@ abstract class TestCase extends \PHPUnit_Framework_TestCase
             'parseValue' => function ($value) { return $value; }, // Allows any value
         ]);
 
+        $invalidScalar = new CustomScalarType([
+            'name' => 'Invalid',
+            'serialize' => function ($value) {
+                return $value;
+            },
+            'parseLiteral' => function ($node) {
+                throw new \Exception('Invalid scalar is always invalid: ' . $node->value);
+            },
+            'parseValue' => function ($node) {
+                throw new \Exception('Invalid scalar is always invalid: ' . $node);
+            },
+        ]);
+
         $queryRoot = new ObjectType([
             'name' => 'QueryRoot',
             'fields' => [
@@ -293,14 +295,16 @@ abstract class TestCase extends \PHPUnit_Framework_TestCase
                 'dogOrHuman' => ['type' => $DogOrHuman],
                 'humanOrAlien' => ['type' => $HumanOrAlien],
                 'complicatedArgs' => ['type' => $ComplicatedArgs],
-                'invalidArg' => [
-                    'args' => ['arg' => ['type' => $invalidScalar]],
-                    'type' => Type::string(),
-                ],
                 'anyArg' => [
                     'args' => ['arg' => ['type' => $anyScalar]],
                     'type' => Type::string(),
                 ],
+                'invalidArg' => [
+                    'args' => [
+                        'arg' => ['type' => $invalidScalar]
+                    ],
+                    'type' => Type::string(),
+                ]
             ]
         ]);
 
diff --git a/tests/Validator/ValidationTest.php b/tests/Validator/ValidationTest.php
index a105bb2..7c7fc09 100644
--- a/tests/Validator/ValidationTest.php
+++ b/tests/Validator/ValidationTest.php
@@ -1,6 +1,7 @@
 <?php
 namespace GraphQL\Tests\Validator;
 
+use GraphQL\Error\FormattedError;
 use GraphQL\Validator\DocumentValidator;
 use GraphQL\Validator\Rules\QueryComplexity;
 
@@ -26,16 +27,32 @@ class ValidationTest extends TestCase
           }
         ');
     }
-/*
-    public function testAllowsSettingRulesGlobally()
-    {
-        $rule = new QueryComplexity(0);
 
-        DocumentValidator::addRule($rule);
-        $instance = DocumentValidator::getRule(QueryComplexity::class);
-        $this->assertSame($rule, $instance);
+    /**
+     * @it detects bad scalar parse
+     */
+    public function testDetectsBadScalarParse()
+    {
+        $doc = '
+      query {
+        invalidArg(arg: "bad value")
+      }
+        ';
+
+        $expectedError = [
+            'message' => "Argument \"arg\" has invalid value \"bad value\".
+Expected type \"Invalid\", found \"bad value\"; Invalid scalar is always invalid: bad value",
+            'locations' => [ ['line' => 3, 'column' => 25] ]
+        ];
+
+        $this->expectInvalid(
+            $this->getTestSchema(),
+            null,
+            $doc,
+            [$expectedError]
+        );
     }
-*/
+
     public function testPassesValidationWithEmptyRules()
     {
         $query = '{invalid}';