diff --git a/src/index.js b/src/index.js
index aecaa4f..8d743d4 100644
--- a/src/index.js
+++ b/src/index.js
@@ -1,5 +1,7 @@
 const ProtoDef = require('./protodef')
-const proto = new ProtoDef()
+// No validation: this instance only supplies the default types export, and
+// validation here would load the validator for every consumer of the package.
+const proto = new ProtoDef(false)
 
 module.exports = {
   ProtoDef,
diff --git a/src/protodef.js b/src/protodef.js
index 0cee5e1..ad6e6d8 100644
--- a/src/protodef.js
+++ b/src/protodef.js
@@ -1,6 +1,5 @@
 const { getFieldInfo, tryCatch } = require('./utils')
 const reduce = require('lodash.reduce')
-const Validator = require('protodef-validator')
 
 function isFieldInfo (type) {
   return typeof type === 'string' ||
@@ -43,7 +42,9 @@ function extendType (functions, defaultTypeArgs) {
 class ProtoDef {
   constructor (validation = true) {
     this.types = {}
-    this.validator = validation ? new Validator() : null
+    // Required here, not at the top: the validator's schema stack (ajv)
+    // must not load when validation is disabled.
+    this.validator = validation ? new (require('protodef-validator'))() : null
     this.addDefaultTypes()
   }