diff --git a/src/Type/Definition/LeafType.php b/src/Type/Definition/LeafType.php
index a36b592..51d6af2 100644
--- a/src/Type/Definition/LeafType.php
+++ b/src/Type/Definition/LeafType.php
@@ -8,4 +8,27 @@ GraphQLEnumType;
 */
 interface LeafType
 {
+    /**
+     * Serializes an internal value to include in a response.
+     *
+     * @param mixed $value
+     * @return mixed
+     */
+    public function serialize($value);
+
+    /**
+     * Parses an externally provided value to use as an input
+     *
+     * @param mixed $value
+     * @return mixed
+     */
+    public function parseValue($value);
+
+    /**
+     * Parses an externally provided literal value to use as an input
+     *
+     * @param \GraphQL\Language\AST\Value $valueAST
+     * @return mixed
+     */
+    public function parseLiteral($valueAST);
 }
diff --git a/src/Type/Definition/ScalarType.php b/src/Type/Definition/ScalarType.php
index 9b9a5a5..afdd367 100644
--- a/src/Type/Definition/ScalarType.php
+++ b/src/Type/Definition/ScalarType.php
@@ -34,28 +34,4 @@ abstract class ScalarType extends Type implements OutputType, InputType, LeafTyp
 
         Utils::invariant($this->name, 'Type must be named.');
     }
-
-    /**
-     * Serializes an internal value to include in a response.
-     *
-     * @param mixed $value
-     * @return mixed
-     */
-    abstract public function serialize($value);
-
-    /**
-     * Parses an externally provided value to use as an input
-     *
-     * @param mixed $value
-     * @return mixed
-     */
-    abstract public function parseValue($value);
-
-    /**
-     * Parses an externally provided literal value to use as an input
-     *
-     * @param \GraphQL\Language\AST\Value $valueAST
-     * @return mixed
-     */
-    abstract public function parseLiteral($valueAST);
 }