diff --git a/package.json b/package.json
index a71445ea..ee431bcc 100644
--- a/package.json
+++ b/package.json
@@ -1,6 +1,6 @@
 {
   "name": "stated-form-bean",
-  "version": "0.1.0-beta.4",
+  "version": "0.1.0-beta.5",
   "description": "",
   "main": "dist/cjs",
   "module": "dist/es",
diff --git a/src/core/FormModel.ts b/src/core/FormModel.ts
index 35163249..d930c35d 100644
--- a/src/core/FormModel.ts
+++ b/src/core/FormModel.ts
@@ -26,10 +26,7 @@ export class FormModel<Values> {
   }
 
   validate<T extends keyof Values>(
-    this: FormModel<Values> &
-      Values & {
-        [ForceUpdate]: (field: T) => void;
-      },
+    this: FormModel<Values> & Values,
     field: T,
     schema?: yup.Schema<Values[T]>,
   ): Promise<boolean> {
@@ -38,7 +35,8 @@ export class FormModel<Values> {
     }
     const formField = this[fields][field];
 
-    const self = this;
+    const self = this as FormModel<Values> &
+      Values & { [ForceUpdate]: (field: T) => void };
     return formField.validate(self[field], schema).then(valid => {
       if (Object.prototype.hasOwnProperty.call(self, ForceUpdate)) {
         self[ForceUpdate](field);