diff --git a/packages/babel-core/src/config/option-assertions.js b/packages/babel-core/src/config/option-assertions.js
index 01c65e4e14..bc0ce7fae6 100644
--- a/packages/babel-core/src/config/option-assertions.js
+++ b/packages/babel-core/src/config/option-assertions.js
@@ -12,6 +12,12 @@ import type {
   RootInputSourceMapOption,
 } from "./options";
 
+export type ValidatorSet = {
+  [string]: Validator<any>,
+};
+
+export type Validator<T> = (string, mixed) => T;
+
 export function assertSourceMaps(
   key: string,
   value: mixed,
diff --git a/packages/babel-core/src/config/option-manager.js b/packages/babel-core/src/config/option-manager.js
index 0c4cd84ffa..20cab68f1c 100644
--- a/packages/babel-core/src/config/option-manager.js
+++ b/packages/babel-core/src/config/option-manager.js
@@ -1,7 +1,7 @@
 // @flow
 
 import * as context from "../index";
-import Plugin from "./plugin";
+import Plugin, { validatePluginObject } from "./plugin";
 import defaults from "lodash/defaults";
 import merge from "lodash/merge";
 import buildConfigChain, { type ConfigItem } from "./build-config-chain";
@@ -28,15 +28,6 @@ type MergeOptions =
       dirname: string,
     };
 
-const ALLOWED_PLUGIN_KEYS = new Set([
-  "name",
-  "manipulateOptions",
-  "pre",
-  "post",
-  "visitor",
-  "inherits",
-]);
-
 export default function manageOptions(opts: {}): {
   options: Object,
   passes: Array<Array<Plugin>>,
@@ -275,37 +266,16 @@ function loadPluginDescriptor(descriptor: BasicDescriptor): Plugin {
 }
 
 const instantiatePlugin = makeWeakCache(
-  (
-    { value: pluginObj, options, dirname, alias }: LoadedDescriptor,
-    cache,
-  ): Plugin => {
-    Object.keys(pluginObj).forEach(key => {
-      if (!ALLOWED_PLUGIN_KEYS.has(key)) {
-        throw new Error(
-          `Plugin ${alias} provided an invalid property of ${key}`,
-        );
-      }
-    });
-    if (
-      pluginObj.visitor &&
-      (pluginObj.visitor.enter || pluginObj.visitor.exit)
-    ) {
-      throw new Error(
-        "Plugins aren't allowed to specify catch-all enter/exit handlers. " +
-          "Please target individual nodes.",
-      );
+  ({ value, options, dirname, alias }: LoadedDescriptor, cache): Plugin => {
+    const pluginObj = validatePluginObject(value);
+
+    const plugin = Object.assign({}, pluginObj);
+    if (plugin.visitor) {
+      plugin.visitor = traverse.explode(clone(plugin.visitor));
     }
 
-    const plugin = Object.assign({}, pluginObj, {
-      visitor: clone(pluginObj.visitor || {}),
-    });
-
-    traverse.explode(plugin.visitor);
-
-    let inheritsDescriptor;
-    let inherits;
     if (plugin.inherits) {
-      inheritsDescriptor = {
+      const inheritsDescriptor = {
         alias: `${alias}$inherits`,
         value: plugin.inherits,
         options,
@@ -313,7 +283,7 @@ const instantiatePlugin = makeWeakCache(
       };
 
       // If the inherited plugin changes, reinstantiate this plugin.
-      inherits = cache.invalidate(() =>
+      const inherits = cache.invalidate(() =>
         loadPluginDescriptor(inheritsDescriptor),
       );
 
@@ -324,8 +294,8 @@ const instantiatePlugin = makeWeakCache(
         plugin.manipulateOptions,
       );
       plugin.visitor = traverse.visitors.merge([
-        inherits.visitor,
-        plugin.visitor,
+        inherits.visitor || {},
+        plugin.visitor || {},
       ]);
     }
 
diff --git a/packages/babel-core/src/config/options.js b/packages/babel-core/src/config/options.js
index 8720dfe267..e47babff92 100644
--- a/packages/babel-core/src/config/options.js
+++ b/packages/babel-core/src/config/options.js
@@ -12,14 +12,10 @@ import {
   assertSourceMaps,
   assertCompact,
   assertSourceType,
+  type ValidatorSet,
+  type Validator,
 } from "./option-assertions";
 
-type ValidatorSet = {
-  [string]: Validator<any>,
-};
-
-type Validator<T> = (string, mixed) => T;
-
 const ROOT_VALIDATORS: ValidatorSet = {
   filename: (assertString: Validator<
     $PropertyType<ValidatedOptions, "filename">,
diff --git a/packages/babel-core/src/config/plugin.js b/packages/babel-core/src/config/plugin.js
index 615a5f5ece..edc251d0ce 100644
--- a/packages/babel-core/src/config/plugin.js
+++ b/packages/babel-core/src/config/plugin.js
@@ -1,43 +1,104 @@
 // @flow
 
-// $FlowIssue recursion?
+import {
+  assertString,
+  assertFunction,
+  assertObject,
+  type ValidatorSet,
+  type Validator,
+} from "./option-assertions";
+
+const VALIDATORS: ValidatorSet = {
+  name: (assertString: Validator<$PropertyType<PluginObject, "name">>),
+  manipulateOptions: (assertFunction: Validator<
+    $PropertyType<PluginObject, "manipulateOptions">,
+  >),
+  pre: (assertFunction: Validator<$PropertyType<PluginObject, "pre">>),
+  post: (assertFunction: Validator<$PropertyType<PluginObject, "post">>),
+  inherits: (assertFunction: Validator<
+    $PropertyType<PluginObject, "inherits">,
+  >),
+  visitor: (assertVisitorMap: Validator<
+    $PropertyType<PluginObject, "visitor">,
+  >),
+};
+
+function assertVisitorMap(key: string, value: mixed): VisitorMap {
+  const obj = assertObject(key, value);
+  if (obj) {
+    Object.keys(obj).forEach(prop => assertVisitorHandler(prop, obj[prop]));
+
+    if (obj.enter || obj.exit) {
+      throw new Error(
+        `.${key} cannot contain catch-all "enter" or "exit" handlers. Please target individual nodes.`,
+      );
+    }
+  }
+  return (obj: any);
+}
+
+function assertVisitorHandler(
+  key: string,
+  value: mixed,
+): VisitorHandler | void {
+  if (value && typeof value === "object") {
+    Object.keys(value).forEach(handler => {
+      if (handler !== "enter" && handler !== "exit") {
+        throw new Error(
+          `.visitor["${key}"] may only have .enter and/or .exit handlers.`,
+        );
+      }
+    });
+  } else if (typeof value !== "function") {
+    throw new Error(`.visitor["${key}"] must be a function`);
+  }
+
+  return (value: any);
+}
+
+type VisitorHandler = Function | { enter?: Function, exit?: Function };
+export type VisitorMap = {
+  [string]: VisitorHandler,
+};
+
+export type PluginObject = {
+  name?: string,
+  manipulateOptions?: Function,
+
+  pre?: Function,
+  post?: Function,
+
+  inherits?: Function,
+  visitor?: VisitorMap,
+};
+
+export function validatePluginObject(obj: {}): PluginObject {
+  Object.keys(obj).forEach(key => {
+    const validator = VALIDATORS[key];
+
+    if (validator) validator(key, obj[key]);
+    else throw new Error(`.${key} is not a valid Plugin property`);
+  });
+
+  return (obj: any);
+}
+
 export default class Plugin {
   key: ?string;
-  manipulateOptions: ?Function;
-  post: ?Function;
-  pre: ?Function;
-  visitor: ?{};
+  manipulateOptions: Function | void;
+  post: Function | void;
+  pre: Function | void;
+  visitor: {};
 
   options: {};
 
-  constructor(plugin: {}, options: {}, key?: string) {
-    if (plugin.name != null && typeof plugin.name !== "string") {
-      throw new Error("Plugin .name must be a string, null, or undefined");
-    }
-    if (
-      plugin.manipulateOptions != null &&
-      typeof plugin.manipulateOptions !== "function"
-    ) {
-      throw new Error(
-        "Plugin .manipulateOptions must be a function, null, or undefined",
-      );
-    }
-    if (plugin.post != null && typeof plugin.post !== "function") {
-      throw new Error("Plugin .post must be a function, null, or undefined");
-    }
-    if (plugin.pre != null && typeof plugin.pre !== "function") {
-      throw new Error("Plugin .pre must be a function, null, or undefined");
-    }
-    if (plugin.visitor != null && typeof plugin.visitor !== "object") {
-      throw new Error("Plugin .visitor must be an object, null, or undefined");
-    }
-
+  constructor(plugin: PluginObject, options: {}, key?: string) {
     this.key = plugin.name || key;
 
     this.manipulateOptions = plugin.manipulateOptions;
     this.post = plugin.post;
     this.pre = plugin.pre;
-    this.visitor = plugin.visitor;
+    this.visitor = plugin.visitor || {};
     this.options = options;
   }
 }